Ceramic heater and ceramic joined article

ABSTRACT

A ceramic heater capable of stably supporting a semiconductor safer and evenly heating the whole of a semiconductor wafer or the like without generating any warp in the semiconductor wafer or the like. The ceramic heater includes a disk-like ceramic substrate, a heating element formed on a surface of or inside the ceramic substrate, and through holes for letting lifter pins pass through the ceramic substrate. The number of the formed through holes is three or more, and the through holes are formed in an area whose distance from the center of the ceramic substrate is ½ or more of the distance from the center to the outer edge of the ceramic substrate.

TECHNICAL FIELD

The present invention mainly relates to a ceramic heater and a ceramicbonded body which are used in the production and inspection ofsemiconductors, the field of optics, and so on.

BACKGROUND ART

Conventionally, a heater, wafer prober or the like wherein a basematerial made of a metal such as stainless steel or aluminum alloy isused has been used in semiconductor producing/inspecting devices and soon, examples of which include an etching device and a chemical vaporphase growth device and the like.

However, such a heater made of metal has the following problems.

First, the thickness of the heater plate must be as thick as about 15 mmsince the heater is made of a metal. Because in a thin metal plate, abend, a strain and so on are generated on the basis of thermal expansionresulting from heating so that a silicon wafer put on the metal plate isdamaged or inclined. However, if the thickness of the heater plate ismade thick, a problem that the heater becomes heavy and bulky arises.

The temperature of a face for heating an object to be heated such as asilicon wafer (referred to as a heating face hereinafter) and the likeis controlled by changing the voltage or current quantity applied to theheating elements. However, since the metal plate is thick, thetemperature of the heater plate does not follow the change in thevoltage or current quantity promptly. Thus, a problem that thetemperature is not easily controlled is caused.

Thus, JP Kokai Hei 11-40330 and so forth suggest a ceramic substratewherein a nitride ceramic or a carbide ceramic, with a high thermalconductivity and a high strength, is used as a substrate and heatingelements formed by sintering metal particles are provided on a surfaceof a plate-form body made of such a ceramic.

As illustrated in FIG. 15, usually, in such a ceramic heater, heatingelements 62 are formed inside a ceramic substrate 61 and further throughholes for passing lifter pins through are formed in the vicinity of thecenter. This is because by letting the lifter pins pass through thethrough holes 65 and then moving the pins up and down, a semiconductorwafer can be relatively easily received from the previous line or thesemiconductor wafer can be carried to the next line. Reference numeral64 represents bottomed holes 64 for embedding temperature measuringelements such as thermocouples, and reference numeral 63 representsexternal terminals for connecting the heating elements 62 to a powersource.

As described above, the through holes 65 are arranged in the vicinity ofthe center of the ceramic substrate 61. This is because in order to workthe lifter pins by means of one motor, it is preferred that thepositions of the lifter pins are closer to each other.

In the case that this ceramic heater 60 is used to heat an object to beheated, such as a semiconductor wafer and the like, the temperaturedistribution in the surface of the ceramic heater 60 is reflected on thesemiconductor wafer or the like if the object is heated in the statethat the object contacts the heating face of the ceramic heater 10. As aresult, it is difficult that the semiconductor wafer or the like isevenly heated.

In order that the surface temperature of the ceramic heater 60 is madeto heat the semiconductor wafer or the like evenly, highly complicatedcontrol is required. Hence, the temperature control is not easy.

Thus, when the semiconductor wafer is heated, there can be usually useda method of supporting the semiconductor wafer by means of the lifterpins provided for carrying the semiconductor wafer. That is, the lifterspins are held in the state that they project slightly from the surfaceof the ceramic substrate 61, and the lifter pins are used to support thesemiconductor wafer in the state that the semiconductor wafer is a givendistance apart from the surface of the ceramic substrate 61. Thesemiconductor wafer is then heated.

According to this method of using the lifter pins, the semiconductorwafer is heated by radiation from the ceramic substrate 61 or convectioncurrent since the semiconductor wafer is held in the state that thesemiconductor wafer is apart from the surface of the ceramic heater 61by the given distance. Accordingly, the temperature distribution in thesurface of the ceramic substrate 61 is not usually reflected directly onthe semiconductor wafer, so that the semiconductor wafer is more evenlyheated and any temperature distribution is not easily generated in thesemiconductor wafer.

However, when the lifter pins are used to intend to carry thesemiconductor wafer, the semiconductor wafer may not be stablysupported. In this case, there arises a problem that the semiconductorwafer is inclined to get out of position.

At the time when a semiconductor wafer or a liquid crystal substrate isput thereon and heated (as well as the time of the state that asemiconductor wafer or a liquid crystal substrate is put on the heatedceramic substrate and until the temperature thereof returns to theoriginal temperature, that is, a transition state), there is caused aproblem that temperature difference is generated in the object to beheated, such as the semiconductor wafer or the liquid crystal substrate.

Moreover, a problem that free particles adhere to the object to beheated is also encountered.

Thus, the present inventors analyzed a cause for which an object to beheated, such a semiconductor wafer or a liquid crystal substrate, (whichmay be referred to as a semiconductor wafer or the like hereinafter), isinclined or temperature unevenness is generated when the semiconductorwafer or the like is heated. As a result, it has been found out that inthe case that the lifter pins concentrate around the center, the objectto be heated, such as the semiconductor wafer cannot be stably supportedand the heat capacity per unit area (volume) in the central portion ofthe ceramic substrate 61 gets smaller than that in the peripheralportion so that the temperature of the central portion of the ceramicsubstrate 61 rises easily at the time of heating the ceramic substrate.

It has also been found out that if the lifter pins are present in thevicinity of the center when a plate-form object to be heated, such as asemiconductor wafer or a liquid crystal substrate, is lifted up, theobject warps and hence the peripheral portion of the object contacts theceramic substrate 61 so that free particles are generated.

When the ceramic heater 60 having these through holes 65 is used to heatan object to be heated such as a semiconductor wafer or a liquid crystalsubstrate, the temperature in the vicinity of the through holes 65locally becomes low. That is, a cooling spot is generated. This resultsin a problem that the temperature of the semiconductor wafer, the liquidcrystal substrate or the like falls in this portion so that thesemiconductor wafer, the liquid crystal substrate or the like is noteasily heated evenly.

Furthermore, JP Kokai Hei 4-324276 suggests a ceramic heater in whichaluminum nitride, which is a non-oxide ceramic having a high thermalconductivity and a large strength, is used as a substrate; heatingelements and conductor filled through holes made of tungsten are made inthis aluminum nitride substrate; and Nichrome wires as externalterminals are brazed thereto.

Since such a ceramic heater has a ceramic substrate having a largemechanical strength at high temperatures, the thickness of the ceramicsubstrate can be made small to make the heat capacity small. As aresult, the temperature of the ceramic substrate can be caused to followchange in the voltage or electric current quantity promptly.

A ceramic heater as described above adopts a means for bonding acylindrical ceramic with a disk-like ceramic to protect wires such asexternal terminals from reactive gas, halogen gas and the like used in asemiconductor producing step, as described in Japanese Patent gazetteNos. 2525974 and 2783980, and JP Kokai 2000-114355.

However, in the case that the ceramic heater described in JapanesePatent gazette No. 2525974 is used, it is exposed to reactive gas,halogen gas and the like for a long time and thermal stress concentrateson the bonding interface between the cylindrical ceramic and thedisk-like ceramic, (which may be referred to as the interfacehereinafter). Thus, by repeating temperature-rising andtemperature-dropping thereof, thermal fatigue is generated, therebycausing a problem that cracks and the like are generated in theinterface and air-tightness of the interface deteriorates so that thewires such as the external terminals are corroded.

In the ceramic heater described in Japanese Patent gazette No. 2783980,in the interface thereof, the ceramic particles grow to extend to bothsides of the interface, whereby the cylindrical ceramic is bonded to thedisk-like ceramic. Therefore, the bonding strength of the interface isstrong but thermal stress concentrates locally. Thus, by repeatingtemperature-rising and temperature-dropping thereof, thermal fatigue isgenerated so that cracks and the like may be generated in the interface,the cylindrical ceramic, or the disk-like ceramic.

For recent semiconductor products, it is required to shorten a timenecessary for throughput. Thus, it is strongly required to shorten atime for rising or dropping the temperature thereof. However, in theceramic heaters described in Japanese Patent gazette No. 2525974, JPKokai Hei 2000-114355 and so forth, a flange portion is formed in thecylindrical ceramic, thereby causing a problem that the thermal capacityincreases and temperature-rising speed drops.

In order to shorten the temperature-rising time, it is necessary toincrease the temperature-rising speed. In order to shorten thetemperature-dropping time, it is necessary to rise thetemperature-dropping speed. However, if the temperature of the ceramicheater is abruptly risen or dropped, larger thermal stress is generatedin the interface and the like. Thus, cracks and the like as describedabove become easy to be generated increasingly.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentionedproblems. An object thereof is to provide a ceramic heater capable ofstably supporting an object to be heated, such as a semiconductor wafer,a liquid crystal substrate and the like, and evenly heating thesemiconductor wafer or the like.

Another object of the present invention is to provide a ceramic heaterwhich prevents the generation of cooling spots, and causes no drop inthe temperature of a semiconductor wafer, a liquid crystal substrate andthe like in the vicinity of through holes formed in a ceramic substrateso that the object to be heated, such as the semiconductor wafer, theliquid crystal substrate and the like can be evenly heated.

Still another object of the present invention is to provide a ceramicbonded body capable of keeping sufficient air-tightness and largelyimproving the reliability thereof because of the face that no thermalstress concentrates locally in the bonding interface between a ceramicbody having a given shape such as a cylindrical shape or a columnarshape and a disk-like ceramic so that no cracks and the like aregenerated in this portion.

In order to attain the above-mentioned objects, a ceramic heateraccording to the first aspect of the present invention comprises: adisk-like ceramic substrate; a heating element formed on a surface of orinside the above-mentioned ceramic substrate; and through holes forletting lifter pins pass through at the above-mentioned ceramicsubstrate, wherein three or more of the above-mentioned through holesare formed, and the above-mentioned through holes are formed in an areawhose distance from the center of the above-mentioned ceramic substrateis ½ or more of the distance from the center of the above-mentionedceramic substrate to the outer edge of the above-mentioned ceramicsubstrate.

According to the above-mentioned ceramic heater, the three or morethrough holes are present in the peripheral portion of the ceramicsubstrate; therefore, the lifter pins, which are passed through thethrough holes, are also present in the peripheral portion of the ceramicsubstrate and do not concentrate in the central portion so that asemiconductor wafer or the like supported by the lifter pins does notbecome unstable. As a result, even if impact and the like are causedwhen the ceramic heater is used, the semiconductor wafer or the likedoes not easily get out of position. Thus, an object to be heated, suchas the semiconductor wafer, can be stably supported by the lifter pins.

In the case that the semiconductor wafer or the like is heated to risethe temperature thereof, a difference in the thermal capacity per unitarea (volume) between the central portion of the ceramic substrate andthe peripheral portion thereof turns into a substantially negligibledegree. As a result, the thermal capacity per unit volume (area) in thecentral portion of the ceramic substrate becomes almost equivalent tothat in the peripheral portion. Thus, the semiconductor wafer or thelike can be evenly heated even at the temperature-rising time thereof(at the transition time).

Furthermore, in the case that the through holes are present in thevicinity of the center, a plate-form object to be heated, such as asemiconductor wafer or a liquid crystal substrate, warps when theplate-form object is pushed up by the lifter pins. Thus, the outercircumference of the plate-form object scrubs the ceramic substratesurface so that free particles are generated. However, according to theceramic heater of the first aspect of the present invention, such aproblem is not caused.

It is desired that the through holes are formed at substantially regularintervals on a single circle having a concentric circle relationshipwith the above-mentioned ceramic substrate. Since the lifter pins passedthrough the through holes are widely dispersed on the ceramic substrateand are arranged at regular intervals, a semiconductor wafer or the likecan be more stably supported. Moreover, the semiconductor wafer or thelike can be kept more horizontally so that the distance between theceramic substrate and the semiconductor wafer or the like is madeconstant. As a result, the semiconductor wafer or the like can be moreevenly heated.

A ceramic heater according to a second aspect of the present inventioncomprises: a disk-like ceramic substrate; a heating element formed on asurface of or inside the above-mentioned ceramic substrate; and throughholes for letting lifter pins pass through at the above-mentionedceramic substrate, wherein the diameter of each of the above-mentionedthrough holes on a heating face side for heating an object to be heatedis larger than the diameter of the above-mentioned through hole on theside opposite to the above-mentioned heating face.

In case the ceramic heater is provided with the through holes forpassing the lifter pins through, the temperature around side walls ofthe through holes drops since the side walls of the through holesusually contact gas having a lower temperature than the substrateitself. As a result, cooling spots are generated in the heating face.

When a semiconductor wafer, a liquid crystal substrate or the like isput on this ceramic heater, in the cooling spots heat is taken away bythe cooling spots; therefore, the temperature in this portion drops sothat evenness in the temperature of the semiconductor wafer, the liquidcrystal substrate and the like is lost.

However, according to the ceramic heater of the second aspect of thepresent invention, the diameter of each of the above-mentioned throughholes on a heating face side for heating an object to be heated islarger than the diameter of the above-mentioned through hole on the sideopposite to the above-mentioned heating face; thus, no solidconstituting the substrate is present in portions where cooling spotsare generated. As a result, the occupation ratio of space becomes largeso that the heat capacity thereof gets small. Accordingly, thetemperature of the semiconductor wafer, the liquid crystal substrate andthe like of the portion in the vicinity of the formed through holeshardly drops, so that the object to be heated, such as the semiconductorwafer or the liquid crystal substrate and the like, can be more evenlyheated.

Regarding the through holes with a diameter on the heating face sidebeing larger than that on the bottom face side, in case the throughholes are constituted so as to have a columnar portion and adiameter-increasing portion having the diameter becoming larger as theportion is closer to the heating face, that is, so as to have a funnelshape, gas having accumulated heat remains in the funnel-shaped portionand cooling spots themselves are not enlarged. Thus, the object to beheated, such as the semiconductor wafer or the liquid crystal substrate,can be more evenly heated.

Since the through holes having the above-mentioned shape can berelatively easily formed with a drill and the like, the through holescan be effectively formed.

The wafer or the like is heated while the space of the above-mentioneddiameter-increasing portion is not filled. This is because when thediameter-increasing portion is filled with a filling member, the ceramicand the filling member are rubbed with each other so that free particlesare generated.

Further, a ceramic bonded body according to a third aspect of thepresent invention includes: a disk-like ceramic substrate inside which aconductor is provided; and a ceramic body bonded to the bottom face ofthe above-mentioned ceramic substrate, wherein the center of an areasurrounded by the interface between the above-mentioned ceramic body andthe above-mentioned ceramic substrate or the center of an areaconstituted by the interface between the above-mentioned ceramic bodyand the above-mentioned ceramic substrate is 3 to 200 μm apart from thecenter of the bottom face of the above-mentioned ceramic substrate.

In the ceramic bonded body according to the third aspect of the presentinvention, the ceramic body may be a columnar body or a plate-form body,or may be a hollow body such as a cylindrical body, or may be a filledbody having a ceramic-filled structure, which has no cavity inside.

FIG. 28 is a sectional view which schematically illustrates a ceramicbonded body 700 using a ceramic body 281 made of a filled body. In theceramic body 281 made of the filled body, external terminals 283 havingsockets 285, and conductive wires 235 are embedded, and further a leadwire 890 of a temperature measuring element 84 is also embedded. FIG. 29is a sectional view which schematically illustrates a ceramic bondedbody 800 using a ceramic body 381 made of a plate-form body. In theceramic body 381 made of the filled body, external terminals 383 havingsockets 385, and conductive wires 335 are embedded, and further a leadwire 890 of a temperature measuring element 84 is also embedded.

In the case of the columnar body, it may be a triangle pole body 150 ora square pole body 160 or may be a polygonal pole body 170, asillustrated in FIGS. 30(a) to 30(c).

In the third aspect of the present invention, the center of the areasurrounded by the interface between the ceramic body and the ceramicsubstrate, or the center of the area constituted by the interfacebetween the ceramic body and the ceramic substrate means the centroid ofa figure constituted by being surrounded by the interface, or thecentroid of a figure constituted by the interface itself.

The centroid is defined as intersection points of straight lines fordividing a figure into two exact halves. In the case of a circle, thecenter of the circle is the centroid.

The most preferred example of the present invention is a ceramic bondedbody including: a disk-like ceramic substrate inside which a conductoris provided; and a ceramic body bonded to the bottom face of the ceramicsubstrate, wherein

-   -   the center of a circle surrounded by the interface between the        cylindrical ceramic body and the ceramic substrate is 3 to 200        μm apart from the center of the bottom face of the ceramic        substrate. Thus, this ceramic bonded body will be described        hereinafter.

For example, in the case of heating a ceramic bonded body wherein thecenter of a circle surrounded by the interface between a cylindricalceramic body and a ceramic substrate, (which may be referred to thecenter A hereinafter), is consistent with the center of the bottom faceof the ceramic substrate, (which may be referred to as the center Bhereinafter), the direction along which the cylindrical ceramic bodyexpands is consistent with the direction along which the ceramicsubstrate expands in the above-mentioned interface. As a result, thermalstress concentrates locally so that thermal fatigue is generated. Thus,cracks and the like are generated.

However, according to the third aspect of the present invention, thatis, the ceramic bonded body wherein the distance between the center Aand the center B, (which may be referred to as the distance L), is from3 to 200 μm apart, when it is heated, the direction along which thecylindrical ceramic body expands is different from the direction alongwhich the ceramic substrate expands. As a result, thermal stress can bedispersed so that the generation of cracks and the like can beprevented.

In the ceramic bonded body having a distance L of less than 3 μm, it isdifficult to disperse thermal stress sufficiently.

If the distance L exceeds 200 μm, thermal stress is converselyconcentrated so that cracks are easily generated. Furthermore, thetemperature distribution in the face for heating a semiconductor wafergets large.

It is desired that the above-mentioned conductor is a heating elementand the ceramic bonded body functions as a ceramic heater.

As described above, this ceramic bonded body has a structure capable ofdispersing thermal stress so that the thermal stress does notconcentrate locally. Thus, even if temperature-rising andtemperature-dropping thereof are repeated, no thermal fatigue isgenerated. In the ceramic bonded body, a flange portion need not beformed in the bonding face between the cylindrical ceramic body and theceramic substrate. Therefore, the thermal capacity does not increase sothat the temperature-dropping speed is not lowered. For this reason, theceramic bonded body can be suitably used as a ceramic heater.

The heating element may be formed into a layer form or into a line form.

Moreover, it is desired that the above-mentioned conductor is anelectrostatic electrode and the above-mentioned ceramic bonded bodyfunctions as an electrostatic chuck.

This is because any electrostatic chuck is used in a corrosiveatmosphere in many cases and a constitution wherein the ceramicsubstrate and the cylindrical ceramic body are bonded to each other asdescribed above is optimal for this chuck.

Additionally, the ceramic substrate desirably has a diameter of 250 mmor more. If the diameter of the ceramic substrate is 250 mm or more, theeffects of the third aspect of the present invention, i.e., the effectsof dispersing thermal stress and preventing the generation of cracks andthe like get larger. This fact can easily be understood from FIG. 32,which shows results of Examples. That is, in the case of the distanceL=0, the generation rate of the cracks is higher as the diameter islarger. When the diameter exceeds 250 mm, the rate abruptly becomeslarge. However, by setting L to 3 μm or 200 μm, the crack generationrate can be suppressed at a low level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bottom face view which schematically illustrates a ceramicheater of a first aspect of the present invention.

FIG. 2 is a partially enlarged sectional view of the ceramic heaterillustrated in FIG. 1.

FIG. 3 is a bottom face view which schematically illustrates anotherexample of the ceramic heater according to the first aspect of thepresent invention.

FIG. 4 is a partially enlarged sectional view of the ceramic heaterillustrated in FIG. 3.

FIGS. 5(a) to 5(d) are sectional views which schematically illustratesome parts of the process for producing the ceramic heater illustratedin FIG. 1.

FIGS. 6(a) to 6(d) are sectional views which schematically illustratesome parts of the process for producing the ceramic heater illustratedin FIG. 3.

FIG. 7 is a graph showing a relationship between temperature differencewhen temperature is risen up and the position of a through hole.

FIG. 8 is a graph showing a relationship between the number of freeparticles and the position of a through hole.

FIG. 9 is a bottom face view which schematically illustrates a ceramicheater of a second aspect of the present invention.

FIG. 10 is a partially enlarged sectional view of the ceramic heaterillustrated in FIG. 9.

FIG. 11 is a bottom face view which schematically illustrates anotherexample of the ceramic heater of the second aspect of the presentinvention.

FIG. 12 is a partially enlarged sectional view of the ceramic heaterillustrated in FIG. 11.

FIGS. 13(a) to 13(d) are sectional views which schematically illustratesome parts of the process for producing the ceramic heater illustratedin FIG. 9.

FIGS. 14(a) to 14(d) are sectional views which schematically illustratesome parts of the process for producing the ceramic heater illustratedin FIG. 11.

FIG. 15 is a bottom face view of a conventional ceramic heater.

FIG. 16 is a graph showing a relationship between temperature difference(ΔT) in a silicon wafer when being heated with a ceramic heateraccording to Example 4 and (the diameter of its diameter-increasingportion in its heating face)/(the diameter of its columnar portion).

FIG. 17(a) is a plan view which schematically illustrates a ceramicbonded body according to a third aspect of the present invention, andFIG. 17(b) is a sectional view of the ceramic bonded body illustrated inFIG. 17(a).

FIG. 18 is a bottom face view which schematically illustrates a ceramicbonded body of the third aspect of the present invention.

FIG. 19 is a sectional view of the ceramic bonded body of the thirdaspect of the present invention.

FIG. 20 is a partially enlarged sectional view which schematicallyillustrates a ceramic substrate constituting the ceramic bonded body ofthe third aspect of the present invention.

FIG. 21 is a vertically sectional view which schematically illustrates aceramic substrate constituting an electrostatic chuck which is anexample of the ceramic bonded body of the third aspect of the presentinvention.

FIG. 22 is a partially enlarged sectional view which schematicallyillustrates a ceramic substrate constituting the electrostatic chuckillustrated in FIG. 21.

FIG. 23 is a horizontally sectional view which schematically illustratesan example of an electrostatic electrode embedded in the ceramicsubstrate.

FIG. 24 is a horizontally sectional view which schematically illustratesanother example of the electrostatic electrode embedded in the ceramicsubstrate.

FIG. 25 is a horizontally sectional view which schematically illustratesstill another example of the electrostatic electrode embedded in theceramic substrate.

FIGS. 26(a) to 26(d) are sectional views which schematically illustratean example of the process for producing a ceramic heater which is anexample of the ceramic bonded body of the third aspect of the presentinvention.

FIG. 27 is a perspective view which schematically illustrates an exampleof the method for bonding a ceramic substrate and a cylindrical ceramicbody.

FIG. 28 is a sectional view which schematically illustrates an exampleof the ceramic bonded body of the third aspect of the present invention.

FIG. 29 is a sectional view which schematically illustrates an exampleof the ceramic bonded body of the third aspect of the present invention.

FIGS. 30(a) to 30(c) are perspective views which illustrate examples ofa columnar body constituting the ceramic bonded body of the third aspectof the present invention.

FIG. 31 is a graph showing results of Test Examples.

FIG. 32 is a graph showing results of Comparative Examples 9 and 10 andExamples 15 and 16.

EXPLANATION OF SYMBOLS

10, 20, 30, 40, 70 ceramic heater 11, 21, 31, 41, 71, 91 ceramicsubstrate 11a, 21a, 31a, 41a, 71a heating face 11b, 21b, 31b, 41b, 71bbottom face 12, 22, 32, 42, 72 heating element 120, 320 conductorcontaining paste layer 130, 330 filled layer 13, 23, 33, 43 externalterminal 13a, 33a, 73, 73′ conductor filled through hole 13b, 33b, 79blind hole 14, 24, 34, 44, 74 bottomed hole 15, 25, 35, 45, 75 throughhole 16, 26, 36, 46 lifter pin 220, 420 metal covering layer 39, 59semiconductor wafer 50, 100, 500 green sheet 77 cylindrical ceramic body

DETAILED DISCLOSURE OF THE INVENTION

First, a ceramic heater according to a first aspect of the presentinvention will be described.

The ceramic heater according to a first aspect of the present inventionincludes a disk-like ceramic substrate; a heating element formed on asurface of or inside the above-mentioned ceramic substrate; and throughholes for letting lifter pins pass through at the above-mentionedceramic substrate, wherein three or more of the above-mentioned throughholes are formed, and the above-mentioned through holes are formed in anarea whose distance from the center of the above-mentioned ceramicsubstrate is ½ or more of the distance from the center of theabove-mentioned ceramic substrate to the outer edge of theabove-mentioned ceramic substrate.

FIG. 1 is a bottom face view which schematically illustrates a ceramicheater according to the first aspect of the present invention. FIG. 2 isa partially enlarged sectional view which schematically illustrates theceramic heater in FIG. 1. In this ceramic heater, heating elements areformed inside its ceramic substrate.

In the ceramic heater 10, the ceramic substrate 11 is formed in adisk-like form. In order to heat the ceramic heater in such a mannerthat the temperature in the whole of a heating face 11 a of the ceramicheater 10 is made even, the heating elements 12 which has aconcentrically circular pattern are formed inside the ceramic substrate11.

Conductor-filled through holes 13 a are formed just under ends ofheating elements 12, and further blind holes 13 b for making theconductor-filled through holes 13 a exposed are formed in the bottomface 11 b. An external terminal 13 is inserted into the blind hole 13 b,and they are bonded to each other with a brazing material and the like(not illustrated). For example, a socket (not illustrated) having aconductive wire is fitted to the external terminal 13. This conductivewire is connected to a power source and the like.

In the bottom face of the ceramic substrate 11, bottomed holes 14 forinserting temperature measuring elements (not illustrated) into areformed.

Furthermore, in the ceramic substrate 11, three through holes 15, forpassing lifter pins 16 through, are formed at regular intervals on acircle whose distance from the center of the ceramic substrate 11 is 55%of the distance from the center to the outer edge thereof.

By moving the lifter pins 16 up and down, a semiconductor wafer or thelike can be relatively easily received from the previous line, and thesemiconductor wafer or the like can be carried to the next line.

Since the semiconductor wafer or the like is not rubbed with the ceramicsubstrate, no free particles are generated from the ceramic substrate.

When the semiconductor wafer 39 is heated, the semiconductor wafer 39can be held and heated in the state that the wafer is a given distanceapart, through the lifter pins 16, from the heating face 11 a of theceramic substrate 11 by being held by the lifter pins 16 in the statethat the pins project slightly from the heating face 11 a of the ceramicsubstrate 11.

By arranging a member having projected structures, such as pins, on thesurface of the ceramic substrate, the semiconductor wafer or the likecan be heated in the state that the semiconductor wafer or the like isapart from the heating face of the ceramic substrate in the same manneras in the case of holding the lifter pins in the state that the lifterpins project slightly from the heating face of the ceramic substrate.

In the ceramic heater according to the first aspect of the presentinvention, the heating elements may be formed inside the ceramicsubstrate or may be formed outside the ceramic substrate.

FIG. 3 is a bottom face view which schematically illustrates anotherexample of the ceramic heater according to the first aspect of thepresent invention. FIG. 4 is a partially enlarged sectional view of theceramic heater in FIG. 3. In this ceramic heater, heating elements areformed on a surface of the ceramic substrate.

In the ceramic heater 20, its ceramic substrate 21 is formed in adisk-like form, and heating elements 22 having a concentrically circularpattern are formed on the surface of the ceramic substrate 21. Externalterminals 23, which are terminals for input and output, are connectedthrough a metal covering layer 220 to both ends of the heating element.

In the bottom face of the ceramic substrate 21, bottomed holes 24, forinserting temperature measuring elements (not illustrated) into, areformed.

Additionally, in the ceramic substrate 21 are formed three through holes25 at regular intervals on a circle whose distance from the center ofthe ceramic substrate 21 is 75% of the distance from the center to theouter edge of the ceramic substrate.

In the same way as in ceramic heater 10, in the ceramic heater 20,lifter pins 26 are passed through the through holes 25 and moved up anddown, whereby a semiconductor wafer or the like can be carried.Moreover, the lifter pins 26 are caused to project from a heating face21 a of the ceramic substrate 21, whereby the semiconductor wafer 39 isheld apart from the ceramic substrate 21 a.

In the ceramic substrate according to the first aspect of the presentinvention, the number of the through holes formed in the ceramicsubstrate is three or more. If the number of the through holes is lessthan 3, that is, 2 or less, it is difficult to support an object to beheated, such as the semiconductor wafer, stably by the lifter pinspassed through the through holes. The number of the through holes is notparticularly limited if the number is 3 or more. However, the number ofthe through holes formed in the ceramic substrate is desirably 11 orless in order to suppress the generation of cooling spots when theceramic heater is used.

The position of the through hole is not particularly limited if thethrough hole is formed in an area whose distance from the center of theceramic substrate is ½ or more of the distance from the center to theouter edge of the ceramic substrate.

However, in order to keep the semiconductor wafer or the likehorizontal, the through hole is desirably formed in an area whosedistance from the center of the ceramic substrate is from 50 to 75% ofthe distance from the center to the outer edge thereof. In the case thatthe through hole is formed in an area whose distance from the center ofthe ceramic substrate exceeds 75% of the distance from the center to theouter edge thereof, the semiconductor wafer or the like can be stablysupported but it is apprehended that the semiconductor wafer or the likewarps since the central portion thereof is not supported.

From the viewpoint that the semiconductor wafer or the like can be morestably supported and can be more evenly heated, the through holes aredesirably formed at substantially regular intervals on a single circlehaving a concentric circle relationship with the ceramic substrate.Since the lifter pins passed through the through holes are widelydispersed in the ceramic substrate and arranged at regular intervals,the semiconductor wafer or the like can be more stably supported andkept in more horizontal manner so that the distance between the ceramicsubstrate and the semiconductor wafer or the like becomes constant. As aresult, the semiconductor wafer or the like can be more evenly heated.

In the case that three through holes described above are formed, thearrangement of the through holes is, for example, as follows: asillustrated in FIG. 1, an arrangement in which three through holes 15are formed at regular intervals on a single circle having a concentriccircle relationship with the ceramic substrate in an area whose distancefrom the center of the ceramic substrate 11 is ½ or more of the distancefrom the center to the outer edge thereof. In the case that four throughholes are formed, an example of the arrangement thereof is anarrangement in which four through holes are formed at regular intervalson a single circle having a concentric circle relationship with theceramic substrate in the same area.

In the case that four or more through holes are formed in the ceramicsubstrate, one of the through holes may be formed at the center of theceramic substrate. When the semiconductor wafer or the like is heldapart from the ceramic substrate by the lifter pins and heated, thecentral portion of the semiconductor wafer or the like can be preventedfrom being warped. As a result, the distance between the semiconductorwafer or the like and the ceramic substrate is formed constant so thatthe semiconductor wafer or the like can be evenly heated.

When the semiconductor wafer or the like is held apart by the lifterpins and heated, the height of the lifter pins passed through thethrough holes, projecting from the heating face of the ceramicsubstrate, is desirably from 5 to 5000 μm, that is, the semiconductorwafer or the like is desirably held in the state that the semiconductorwafer or the like is from 5 to 5000 μm apart from the heating face ofthe ceramic substrate. If the height is less than 5 μm, the temperatureof the semiconductor wafer or the like is affected by the temperaturedistribution in the ceramic substrate and made uneven. If the heightexceeds 5000 μm, the temperature of the semiconductor wafer or the likedoes not rise easily. As a result, in particular, the temperature of theperipheral portion of the semiconductor wafer or the like becomes low.

The object to be heated and the heating face of the ceramic substrateare desirably from 5 to 500 μm, more desirably from 20 to 200 μm apartfrom each other.

The shape of the through holes and the lifter pins, as viewed in plan,is usually a circular shape. About the through holes, their diameter onthe heating face side, which heats the object to be heated, may belarger than that on the bottom face side. This is because the heatcapacity of the portion where cooling spots are easily generated can belargely lowered so that the semiconductor wafer can be more evenlyheated.

Furthermore, the diameter of the through holes is desirably from 1 to100 mm, more desirably from 1 to 20 mm. If the diameter is less than 1mm, the semiconductor wafer or the like cannot be stably put on thelifter pins since the lifter pins passed through the through holes aretoo thin. On the other hand, if the diameter exceeds 100 mm, coolingspots are generated in the heating face of the ceramic heater since thethrough holes are too large. As a result, it is apprehended that thesemiconductor wafer or the like cannot be evenly heated.

The diameter of the lifter pins is desirably substantially equal to thatof the through holes for letting the lifter pins pass through. When thediameter of the lifter pins is largely different from that of thethrough holes, that is, when the diameter of the lifter pins is farsmaller than that of the through holes, gaps are generated between thelifter pins and the side walls of the through holes. Accordingly, heatis radiated from the gaps so that cooling spots are generated in theheating face of the ceramic heater. Thus, it is apprehended that thesemiconductor wafer or the like cannot be evenly heated.

In the ceramic heater according to the first aspect of the presentinvention, the diameter of the ceramic substrate is desirably 200 mm ormore for the following reason: as the diameter of the ceramic heater islarger, the semiconductor wafer or the like having a larger diameter,which warps more easily, can be placed; therefore, the constitution ofthe first aspect of the present invention functions effectively.

The diameter of the ceramic substrate is desirably 12 inches (300 mm) ormore. This size is a size which becomes the main current ofsemiconductor wafers in the next generation.

The thickness of the ceramic substrate is desirably 25 mm or less. Thisis because the temperature-following character deteriorates if thethickness of the ceramic substrate exceeds 25 mm. The thickness isdesirably 0.5 mm or more. If the thickness is less than 0.5 mm, theceramic substrate is more easily broken since the strength itself of theceramic substrate drops. More desirably, the thickness exceeds 1.5 and 5mm or less. If the thickness is more than 5 mm, heat is not easilyconducted so that the heating efficiency trends to deteriorate. On theother hand, if the thickness is 1.5 mm or less, a temperaturedistribution is generated in the heating face since heat conducted inthe ceramic substrate does not diffuse sufficiently. Additionally, thestrength of the ceramic substrate drops so that it may be broken.

In the ceramic heater according to the first aspect of the presentinvention, it is desired that a bottomed hole extending from the sideopposite to the heating face, on which an object to be heated are put,to the heating face is formed in the ceramic substrate and further thebottom of the bottomed hole is formed relatively closer to the heatingface than to the heating elements and a temperature measuring element(not illustrated), such as a thermocouple, is fitted to this bottomedhole.

The distance between the bottom of the bottomed hole and the heatingface is desirably from 0.1 mm to ½ of the thickness of the ceramicsubstrate.

In this way, a temperature-measuring position is closer to the heatingface than the heating elements, so that the temperature of thesemiconductor wafer or the like can be more precisely measured.

If the distance between the bottom of the bottomed hole and the heatingface is less than 0.1 mm, heat is radiated at the point so that atemperature distribution is formed in the heating face. If the distanceexceeds ½, the ceramic substrate is easily affected by the temperatureof the heating elements so that temperature-control cannot be performed.Thus, a temperature distribution is formed as well in the heating face.

The diameter of the bottomed hole desirably ranges from 0.3 to 5 mm. Ifthe diameter is too large, the heat-radiating property becomes large. Ifthe diameter is too small, the workability deteriorates so that thedistance to the heating face cannot be made even.

A plurality of the bottomed holes are desirably arranged symmetricallywith the center of the ceramic substrate and arranged into a cross form.This is because temperatures in the entire heating face can be measured.

Examples of the temperature measuring element include a thermocouple, aplatinum temperature measuring resistor, a thermistor and the like.

Examples of the thermocouple include K, R, B, S, E, J and T typethermocouples, as described in JIS-C-1602 (1980). Of these, the K typethermocouple is preferred.

Desirably, the size of the connecting part of the thermocouple is equalto or more than the strand diameter thereof, and is 0.5 mm or less. Thisis because if the connecting part is large, the heat capacity is largeso that the responsibility deteriorates. It is difficult that the sizeis made smaller than the strand diameter.

The above-mentioned temperature measuring element may be bonded to thebottom of the bottomed hole with brazing gold, brazing silver and thelike or, the above-mentioned temperature measuring element may beinserted into the bottomed hole followed by the step of sealing thebottomed holes with a heat-resistant resin. The two may be usedtogether. Examples of the heat-resistant resin include thermosettingresins, in particular, epoxy resin, polyimide resin,bismaleimide-triazine resin and the like. These resins may be used aloneor in combination of two or more.

As the above-mentioned brazing gold, desired is at least one selectedfrom an alloy of 37 to 80.5% by weight of Au and 63 to 19.5% by weightof Cu, and an alloy of 81.5 to 82.5% by weight of Au and 18.5 to 17.5%by weight of Ni. These have a melting temperature of 900° C. or more,and are not easily melted in high temperature regions.

Examples of the brazing silver include Ag-Cu types.

The material of the ceramic substrate constituting the ceramic heateraccording to the first aspect of the present invention is notparticularly limited. For example, a nitride ceramic or a carbideceramic is desirable. Since a nitride ceramic or a carbide ceramic has asmaller thermal expansion coefficient than metals and a far highermechanical strength than metals, the ceramic substrate thereof does notwarp or bend even if the thickness thereof is made small. Therefore, theceramic substrate can be made thin and light. Since the thermalconductivity of the ceramic substrate is high and the ceramic substrateitself is thin, the surface temperature of the ceramic substrate followstemperature change in the heating elements promptly. That is, thesurface temperature of the ceramic substrate can be controlled bychanging voltage or electric current quantity to change the temperatureof the heating elements.

Examples of the nitride ceramic include aluminum nitride, siliconnitride, boron nitride, titanium nitride and the like. These may be usedalone or in combination of two or more.

Examples of the carbide ceramic include silicon carbide, zirconiumcarbide, titanium carbide, tantalum carbide, tungsten carbide and thelike. These may be used alone or in combination of two or more.

Of these, aluminum nitride is most preferred. This is because itsthermal conductivity is highest, that is, 180 W/m·K and aluminum nitridehas superior temperature-following character.

When a nitride ceramic, a carbide ceramic and the like are used as theceramic substrate, an insulating layer maybe formed if necessary. Abouta nitride ceramic, the volume resistance value thereof drops easily athigh temperatures by solid-solution of oxygen and the like, and acarbide ceramic has an electric conductivity so far as the ceramic isnot made into high purity. By making the insulating layer, a shortcircuit is prevented between the circuits at high temperatures or evenif it contains impurities. Thus, the temperature controllability can beensured.

The above-mentioned insulating layer is desirably an oxide ceramic.Specifically, silica, alumina, mullite, cordierite, beryllia, and thelike can be used.

Such an insulating layer may be formed by spin-coating the ceramicsubstrate with a sol solution wherein an alkoxide is hydrolyzed andpolymerized, and then drying and firing the solution, or by sputtering,CVD and the like. The surface of the ceramic substrate may be subjectedto oxidization-treatment to deposit an oxide layer.

The insulating layer is desirably from 0.1 to 1000 μm in thickness. Ifthe thickness is less than 0.1 μm, insulating property cannot beensured. If the thickness exceeds 1000 μm, heat conductivity from theheating elements to the ceramic substrate is hindered.

Furthermore, the volume resistivity of the insulating layer is desirably10 or more times larger than that of the above-mentioned ceramicsubstrate (at the same measurement temperature). In the case of lessthan 10 times, a short circuit between the circuits cannot be prevented.

It is desired that the ceramic substrate contains carbon and the carboncontent is from 200 to 5000 ppm. This is because the electrodes can beconcealed and black-body radiation is easily used.

The brightness of the ceramic substrate is desirably N6 or less as avalue based on the rule of JIS Z 8721. This is because the ceramichaving such a brightness is superior in radiant heat capacity and theproperty of the concealing.

The brightness N is defined as follows: the brightness of ideal black ismade to 0; that of ideal white is made to 10; respective colors aredivided into 10 parts in the manner that the brightness of therespective colors is recognized stepwise between the brightness of blackand that of white; and the resultant parts are indicated by symbols N0to N10, respectively.

Actual measurement thereof is performed by comparison with color signalscorresponding to N0 to N10. One place of decimals in this case is madeto 0 or 5.

When the heating elements are disposed, they may be formed on thesurface (bottom face) of the ceramic substrate or may be embedded in theceramic substrate.

When the heating elements are formed inside the ceramic substrate, it isdesired that the heating elements are formed at positions having adistance, from the face opposite to the heating face, of 60% or less ofthe thickness. In the case of more than 60%, heat conducted in theceramic substrate does not diffuse sufficiently since the heatingelements are too close to the heating face. Thus, a temperaturedispersion in the heating face is generated.

When the heating elements are formed inside the ceramic substrate, aplurality of heating element forming layers may be formed. In this case,the patterns of the respective layers are desirably in the state thatany one of the heating elements is formed on some layer so as to becomplementary to each other and, when viewed from a position above theheating surface, the patterns are formed in all areas. An example ofsuch a structure having a staggered relation.

The heating elements may be set inside the ceramic substrate and theheating elements may be partially formed exposed.

When the heating elements are formed on the surface of the ceramicsubstrate, the heating face is desirably on the side opposite to theface on which the heating elements are formed. This is becausetemperature evenness in the heating face can be improved since theceramic substrate plays a role for thermal diffusion.

When the heating elements are formed on the surface of the ceramicsubstrate, the following method is preferred: a method of applying aconductor containing paste which contains metal particles to the surfaceof the ceramic substrate to form a conductor containing paste layerhaving a given pattern, and firing this to sinter the metal particles onthe surface of the ceramic substrate. If the metal particles are meltedand adhered to each other and the metal particles and the ceramic aremelted and adhered to each other in the sintering of the metal, thesintering is sufficient.

When the heating elements are formed inside the ceramic substrate, thethickness thereof is preferably from 1 to 50 μm. When the heatingelements are formed on the surface of the ceramic substrate, thethickness of the heating elements is preferably from 1 to 30 μm, morepreferably from 1 to 10 μm.

When the heating elements are formed inside the ceramic substrate, thewidth of the heating elements is preferably from 5 to 20 μm. When theheating elements are formed on the surface of the ceramic substrate, thewidth of the heating elements is preferably from 0.1 to 20 mm, morepreferably from 0.1 to 5 mm.

The resistance value of the heating elements can be changed dependentlyon their width or thickness. The above-mentioned ranges are however mostpractical. The resistance value becomes larger as the heating elementsbecome thinner and narrower. The thickness and the width of the heatingelements become larger in the case that the heating elements are formedinside the ceramic substrate. However, when the heating elements areformed inside, the distance between the heating surface and the heatingelements becomes short so that the evenness of the temperature in thesurface deteriorates. Thus, it is necessary to make the width of theheating elements themselves large. Since the heating elements are formedinside, it is unnecessary to consider the adhesiveness to a nitrideceramic and the like ceramic. Therefore, it is possible to use a highmelting point metal such as tungsten or molybdenum, or a carbide oftungsten, molybdenum and the like. Thus, the resistance value can bemade high. Therefore, the thickness itself may be made large in order toprevent wire-snapping and so on. For these reasons, the heating elementsare desirably formed to have the above-mentioned thickness and width.

By setting the position where the heating elements are formed in thisway, heat generated from the heating elements diffuses to the whole ofthe ceramic substrate while the heat is conducted. Thus, a temperaturedistribution in the face for heating an object to be heated (asemiconductor wafer or the like) is made even so that the temperaturesof respective portions of the object to be heated are made even.

As the pattern of the heating elements in the ceramic heater accordingto the first aspect of the present invention, for example, a spiralpattern, an eccentrically circular pattern, a pattern of repeatedbending lines and the like can be used, as well as the concentricallycircular pattern illustrated in FIG. 1. These may be used together.

By making the heating element pattern formed in the outermostcircumference into a pattern divided in the circumferential direction,minute temperature control can be attained in the outermostcircumference of the ceramic heater, the temperature of which is readilylowered. Thus, any distribution in the temperature of the ceramic heatercan be suppressed. Furthermore, the heating element pattern divided inthe circumferential direction may be formed not only in the outermostcircumference of the ceramic substrate but also inside it.

The heating elements may have a rectangular section or an ellipticalsection. They desirably have a flat section. From the flat section, heatis more easily radiated toward the heating face. Thus, a temperaturedistribution in the heating face is not easily generated.

The aspect ratio (the width of the heating element/the thickness of theheating element) of the section is desirably from 10 to 5000.

Adjusting the aspect ratio into this range makes it possible to increasethe resistance value of the heating elements and keep the evenness ofthe temperature in the heating face.

In the case that the thickness of the heating elements is made constant,the amount of heat conducted toward the heating face of the ceramicsubstrate becomes small if the aspect ratio is smaller than theabove-mentioned range. Thus, a heat distribution similar to the patternof the heating elements is generated in the heating face. On the otherhand, if the aspect ratio is too large, the temperature of the portionsjust above the centers of the heating elements becomes high so that aheat distribution similar to the pattern of the heating elements isgenerated in the heating face. Accordingly, if temperature distributionis considered, the aspect ratio of the section is preferably from 10 to5000.

When the heating elements are formed on the surface of the ceramicsubstrate, the aspect ratio is desirably from 10 to 200. When theheating elements are formed inside the ceramic substrate, the aspectratio is desirably from 200 to 5000.

The aspect ratio becomes larger in the case that the heating elementsare formed inside the ceramic substrate. This is based on the followingreason. If the heating elements are formed inside, the distance betweenthe heating face and the heating elements becomes short so thattemperature evenness in the surface deteriorates. It is thereforenecessary to make the heating elements themselves flat.

A conductor containing paste used when the heating elements are formedis not particularly limited. Preferably, the paste contains a resin, asolvent, a thickener and the like as well as metal particles or aconductive ceramic for ensuring electric conductivity.

The above-mentioned metal particles are preferably made of, for example,a noble metal (gold, silver, platinum or palladium), lead, tungsten,molybdenum, nickel and the like. Of these, the noble metal (gold,silver, platinum or palladium) is more preferred. These may be usedalone, but are desirably used in combination of two or more. Thesemetals are not relatively easily oxidized, and have a resistance valuesufficient for generating heat.

Examples of the above-mentioned conductive ceramic include carbides oftungsten and molybdenum. These may be used alone or in combination oftwo or more.

The particle diameter of these metal particles or the conductive ceramicparticles is preferably from 0.1 to 100 μm. If the particle diameter istoo fine, that is, less than0.1 μm, they are easily oxidized. On theother hand, if the particle diameter exceeds 100 μm, they are not easilysintered so that the resistance value becomes large.

The shape of the metal particles may be spherical or scaly. When thesemetal particles are used, they maybe a mixture of spherical particlesand scaly particles.

In the case that the metal particles are scaly or a mixture of sphericalparticles and scaly particles, metal oxides between the metal particlesare easily held and adhesion between the heating elements and thenitride ceramic and the like is made sure. Moreover, the resistancevalue can be made large. Thus, this case is profitable.

Examples of the resin used in the conductor containing paste includeepoxy resin, phenol resin and the like. Examples of the solvent areisopropyl alcohol and the like. Examples of the thickener is celluloseand the like.

It is desired to add a metal oxide to the metal particles in theconductor-containing paste and form the heating elements up to asintered body of the metal particles and the metal oxide, as describedabove. By sintering the metal oxide together with the metal particles inthis way, the nitride ceramic or the carbide ceramic constituting theceramic substrate can be closely adhered to the metal particles.

The reason why the adhesion to the nitride ceramic or the carbideceramic by mixing the metal oxide is improved is unclear, but would bebased on the following. The surface of the metal particles, or thesurface of the nitride ceramic or the carbide ceramic is slightlyoxidized so that an oxidized film is formed. Pieces of this oxidizedfilm are sintered and integrated with each other through the metal oxideso that the metal particles and the nitride ceramic or the carbideceramic are closely adhered to each other.

A preferred example of the above-mentioned metal oxide is at least oneselected from the group consisting of lead oxide, zinc oxide, silica,boron oxide (B₂O₃), alumina, yttria and titania.

These oxides make it possible to improve adhesion between the metalparticles and the nitride ceramic or the carbide ceramic withoutincreasing the resistance value of the heating elements.

When the total amount of the metal oxides is set to 100 parts by weight,the weight ratio of lead oxide, zinc oxide, silica, boron oxide (B₂O₃),alumina, yttria and titania is as follows: lead oxide: 1 to 10, silica:1 to 30, boron oxide: 5 to 50, zinc oxide: 20 to 70, alumina: 1 to 10,yttria: 1 to 50 and titania: 1 to 50. The weight ratio is desirablyadjusted within the scope that the total thereof does not exceed 100parts by weight.

By adjusting the amounts of these oxides within these ranges, inparticular, adhesion to the nitride ceramic can be improved.

The amount of the metal oxide added in the metal particles is preferably0.1% or more by weight and less than 10% by weight.

As the heating elements, a metal foil or a metal wire may be used. Asthe metal foil, a nickel foil or stainless steel foil formed intoheating elements by patterning based on etching and the like ispreferred. The patterned metal foil may be stuck with a resin film andthe like. Examples of the metal wire include a tungsten wire and amolybdenum wire.

The area resistivity when the heating elements are formed is preferablyfrom 1 mΩ/□ to 10 Ω/□. If the area resistivity is less than 0.1 Ω/□, theresistivity is too small so that the heat quantity is small. Thus, theheating elements do not exhibit its original function easily. On theother hand, if the area resistivity exceeds 10 Ω/□, the heat quantitybecomes too large for applied voltage quantity. Thus, in the ceramicsubstrate wherein the heating elements are formed on the surface of theceramic substrate, the heat quantity thereof is not easily controlled.From the viewpoint of the control of the heat quantity, the arearesistivity of the heating elements is more preferably from 1 to 50mΩ/□. However, if the area resistivity is made large, the pattern width(sectional area) can be made large so that a problem ofwire-disconnection is not easily caused. Therefore, the area resistivityis preferably set to 50 mΩ/□ as the case may be.

In the case that the heating elements are formed on the surface of theceramic substrate 21, a metal covering layer 220 (see FIG. 4) ispreferably formed on the surface of the heating elements. The metalcovering layer prevents a change in the resistance value based onoxidization of the inner metal sintered body. The thickness of theformed metal covering layer 220 is preferably from 0.1 to 10 μm.

The metal used when the metal covering layer 220 is formed is notparticularly limited if the metal is a non-oxidizable metal. Specificexamples thereof include gold, silver, palladium, platinum, and nickel.These may be used alone or in combination of two or more. Of thesemetals, nickel is preferred.

In the heating element 12, a terminal for connection to a power sourceis necessary. This terminal is fixed to the heating element 12 throughsolder. Nickel prevents thermal diffusion from the solder. An example ofthe connecting terminal is an external terminal 13 made of kovar.

In the case that the heating elements are formed inside the ceramicsubstrate, no covering is necessary since the surface of the heatingelements is not oxidized. In the case that the heating elements areformed inside the ceramic substrate 11, a part of the heating elementsmay be exposed in the surface. It is allowable that conductor filledthrough holes for connecting the heating elements are formed in theterminal portions and terminals are connected and fixed to the conductorfilled through holes.

In the case that the connecting terminals are connected, an alloy suchas silver-lead, lead-tin or bismuth-tin can be used as the solder. Thethickness of the solder layer is desirably from 0.1 to 50 μm. This isbecause this range is a range sufficient for maintaining connectionbased on the solder.

The ceramic heater according to the first aspect of the presentinvention can be used within the temperature range of 100 to 800° C.

A ceramic body having a cylindrical shape or the like may be bonded tothe bottom face of the ceramic substrate constituting the ceramic heateraccording to the first aspect of the present invention so as to protectwires such as external terminals. In this way, the wires such asexternal terminals can be prevented from being corroded by reactive gas,halogen gas and the like.

Furthermore, the ceramic heater according to the first aspect of thepresent invention can be used when a liquid crystal substrate is heated.

The following will describe a process for producing the ceramic heateraccording to the first aspect of the present invention.

Firstly, a process for producing a ceramic heater wherein heatingelements 12 are formed inside a ceramic substrate 11 (see FIGS. 1 and 2)will be described on the basis of FIG. 5.

(1) Step of Forming the Ceramic Substrate

First, powder of a nitride ceramic and the like is mixed with a binder,a solvent and so on to prepare a paste. This is used to form greensheets 50.

As the above-mentioned ceramic powder, aluminum nitride, and the likecan be used. If necessary, a sintering aid such as yttria, a compoundcontaining Na or Ca, and the like may be added thereto.

As the binder, desirable is at least one selected from an acrylic resinbinder, ethylcellulose, butylcellosolve, and polyvinyl alcohol.

As the solvent, desirable is at least one selected from α-terpineol andglycol.

A paste obtained by mixing these is formed into a sheet form by a doctorblade process, to manufacture green sheets.

The thickness of the green sheets is preferably from 0.1 to 5 mm.

(2) Step of Printing a Conductor Containing Paste on the Green Sheet

A metal paste or a conductor containing paste containing a conductiveceramic, for forming heating elements 12, is printed on the green sheet50, so as to form a conductor containing paste layer 120. A conductorcontaining paste filled layer 130 for conductor filled through holes 13a is formed in through holes.

The conductor containing paste contains metal particles or conductiveceramic particles.

The average particle diameter of tungsten particles or molybdenumparticles is preferably from 0.1 to 5 μm. If the average particle isless than 0.1 μm or exceeds 5 μm, the conductor containing paste is noteasily printed.

Such a conductor containing paste may be a composition (paste) obtainedby mixing, for example, 85 to 87 parts by weight of the metal particlesor the conductive ceramic particles; 1.5 to 10 to parts by weight of atleast one binder selected from acrylic resin binders, ethylcellulose,butylcellosolve and polyvinyl alcohol; and 1.5 to 10 parts by weight ofat least one solvent selected from α-terpineol and glycol.

(3) Step of Laminating the Green Sheets

Green sheets 50 on which no conductor containing paste is printed arelaminated on the upper and lower sides of the green sheet 50 on whichthe conductor containing paste is printed (see FIG. 5(a)).

At this time, the laminating is performed in such a manner that thegreen sheet 50 on which the conductor containing paste is printed isarranged at a position which has a distance, from the bottom face, of60% or less of the thickness of the laminated green sheets.

Specifically, the number of the green sheets laminated on the upper sideis preferably from 20 to 50, and that of the green sheets laminated onthe lower side is preferably from 5 to 20.

(4) Step of Firing the Green Sheet Lamination

The green sheet lamination is heated and pressed to sinter the greensheets and the inner conductor containing paste layer. The heatingtemperature is preferably from 1000 to 2000° C., and the pressingpressure is preferably from 10 to 20 MPa. The heating is performed inthe atmosphere of an inert gas. As the inert gas, argon, nitrogen andthe like can be used.

Next, three or more through holes 15, for letting lifter pins 16 forsupporting a semiconductor wafer 39 pass through, are formed in theresultant sintered body. The holes 15 are formed in an area whosedistance from the center of the ceramic substrate is ½ or more of thedistance from the center to the outer edge of the ceramic substrate.

The through holes 15 are desirably formed at substantially regularintervals on a single circle having a concentric circle relationshipwith the ceramic substrate 11 for the following reason: the lifter pins,which are passed through the through holes 15, are widely dispersed onthe ceramic substrate 11 and arranged at regular interval; therefore,the semiconductor wafer 39 can be kept more horizontal and the distancebetween the ceramic substrate 11 and the semiconductor wafer 39 is madeconstant, so that the semiconductor wafer 39 can be more evenly heated.

Furthermore, bottomed holes 14, for embedding temperature measuringelements such as thermocouples, are formed in the ceramic substrate (seeFIG. 5(b)). Thereafter, blind holes 13 are provided to make theconductor filled through holes 13 a, for connecting the heating elements12 to external terminals 13, exposed (see FIG. 5(c)).

The above-mentioned steps of making the bottomed holes and the throughholes may be applied to the above-mentioned sheet lamination, but ispreferably applied to the above-mentioned sintered body. This is becausethe lamination may be deformed in the sintering step.

The through holes and the bottomed holes can be formed by grinding thesurface and then subjecting the surface to blast treatment such assandblast. The external terminals 13 are connected to the conductorfilled through holes 13 a for connecting the inner heating elements 12,and heated for re-flow. The heating temperature is preferably from 200to 500° C.

Furthermore, thermocouples (not illustrated) as temperature measuringelements are fitted into the bottomed holes 14 with brazing silver,brazing gold and the like, and then holes are sealed up with aheat-resistant resin such as polyimide, so as to finish the productionof a ceramic heater 10 (see FIG. 5(d)).

The following will describe a process for producing a ceramic heater 20wherein heating elements 22 are formed on the bottom face of a ceramicsubstrate 21 (see FIGS. 3 and 4) on the basis of FIG. 6.

(1) Step of Forming the Ceramic Substrate

A sintering aid such as yttria (Y₂O₃) or B₄C, a compound containing Naor Ca, a binder and so on are blended as appropriate with powder made ofa ceramic such as a nitride ceramic, for example, the above-mentionedaluminum nitride or a carbide ceramic, so as to prepare a slurry.Thereafter, this slurry is made into a granular form by spray drying andthe like. The granules are put into a mold and pressed to be formed intoa plate form or some other form. Thus, a raw formed body (green) isproduced.

Next, this raw formed body is heated and fired to be sintered. Thus, aplate made of the ceramic is produced. Thereafter, the plate is madeinto a given shape to produce the ceramic substrate 21. The shape of theraw formed body may be such a shape that the sintered body can be usedas it is after the firing (FIG. 6(a)). By heating and firing the rawformed body under pressure, the ceramic substrate 21 having no pores canbe produced. It is sufficient that the heating and the firing areperformed at the sintering temperature or higher. The firing temperatureis from 1000 to 2500° C. for nitride ceramics or carbide ceramics. Thefiring temperature is from 1500 to 2000° C. for oxide ceramics.

Furthermore, the ceramic substrate is drilled so as to form three ormore through holes 25 for letting lifter pins 26 for supporting asemiconductor wafer 39 pass through, in an area whose distance from thecenter of the ceramic substrate is ½ or more of the distance from thecenter to the outer edge of the ceramic substrate.

In the same manner as in the ceramic substrate 10, the through holes 25are desirably formed at substantially regular intervals on a singlecircle having a concentric circle relationship with the ceramicsubstrate 21.

Additionally, bottomed holes 24, for embedding temperature measuringelements such as thermocouples, are formed in the ceramic substrate (seeFIG. 6(a)).

(2) Step of Printing a Conductor Containing Paste on the CeramicSubstrate

A conductor containing paste is generally a fluid comprising metalparticles, a resin and a solvent, and having a high viscosity. Thisconductor containing paste is printed on portions where heating elements22 are to be formed by screen printing and the like. In this way, aconductor containing paste layer is formed.

The conductor containing paste is desirably formed in such a manner thatsections of the heating elements 22 subjected to the firing arerectangular and flat.

(3) Firing of the Conductor Containing Paste

The conductor containing paste layer printed on the bottom face 21 b ofthe ceramic substrate is heated and fired to remove the resin and thesolvent and sinter the metal particles. Thus, the metal particles arebaked onto the bottom face of the ceramic substrate 21 to form theheating elements 22 (FIG. 6(b)). The heating and firing temperature ispreferably from 500 to 1000° C.

If the above-mentioned oxides are added to the conductor containingpaste, the metal particles, the ceramic substrate and the oxides aresintered to be integrated with each other. Thus, the adhesivenessbetween the heating elements 22 and the ceramic substrate 21 isimproved.

(4) Step of Forming a Metal Covering Layer

Next, a metal covering layer 220 is deposited on the surface of theheating elements 22 (see FIG. 6(c)). The metal covering layer 220 can beformed by electroplating, electroless plating, sputtering and the like.From the viewpoint of mass-productivity, electroless plating is optimal.

(5) Fitting of Terminals and so on

A terminal (external terminal 23) for connection to a power source isfitted up to an end of each of the pattern pieces of the heatingelements 22 with solder. Thermocouples (not illustrated) are fixed tothe bottomed holes 24 with brazing silver, brazing gold and the like.The bottomed holes are sealed with a heat-resistant resin such aspolyimide and the like, so as to finish the production of a ceramicheater 20 (see FIG. 6(d)).

About the ceramic heater according to the first aspect of the presentinvention, electrostatic electrodes are set inside the ceramicsubstrate, whereby the ceramic substrate can be used as an electrostaticchuck.

By forming a chuck top conductive layer on the surface, the ceramicheater can be used as a ceramic substrate for a wafer prober.

As described above, the ceramic heater according to the first aspect ofthe present invention can be used as a ceramic heater for asemiconductor producing/inspecting device or for heating a liquidcrystal substrate.

Next, a ceramic heater according to a second aspect of the presentinvention will be described.

The ceramic heater according to the second aspect of the presentinvention includes: a disk-like ceramic substrate; a heating elementformed on a surface of or inside the ceramic substrate; and throughholes for letting lifter pins into at the ceramic substrate, wherein thediameter of each of the above-mentioned through holes on a heating faceside for heating an object to be heated is larger than the diameter ofthe above-mentioned through hole on the side opposite to theabove-mentioned heating face.

In the ceramic heater according to the second aspect of the presentinvention, the diameter on the heating face side of the through holes isdesirably from 1.2 to 10 times the diameter on the side opposite to theheating face. If the diameter on the heating side is less than 1.2 timesthe diameter on the side opposite to the heating face or exceeds 10times, the effect of accumulating heat cannot be obtained.

FIG. 9 is a plan view which schematically illustrates a ceramic heateraccording to the second aspect of the present invention. FIG. 10 is apartially enlarged sectional view which schematically illustrates theceramic heater in FIG. 9. In this ceramic heater, heating elements areformed inside its ceramic substrate.

In this ceramic heater 30, the ceramic substrate 31 is formed in adisk-like form. In order to heat the ceramic heater in such a mannerthat the temperature in the whole of a heating face 31 a of the ceramicheater 30 is made even, the heating elements 32 which has aconcentrically circular pattern are formed inside the ceramic substrate31.

Conductor filled through holes 33 a are formed just under ends ofheating elements 32, and further blind holes 33 b for making theconductor filled through holes 33 a exposed are formed in the bottomface 31 b. An external terminal 33 is inserted into the blind hole 33 b,and they are bonded to each other with a brazing material (notillustrated). For example, a socket (not illustrated) having aconductive wire is fitted to the external terminal 33. This conductivewire is connected to a power source and the like.

In the bottom face of the ceramic substrate 31, bottomed holes 34, forinserting temperature measuring elements (not illustrated) into, areformed.

Furthermore, three through holes 35, for letting lifter pins 36 passthrough, are formed in the vicinity of the center of the ceramicsubstrate 31.

As illustrated in FIG. 10, the through hole 35 is composed of a columnarportion 35 a and a diameter-increasing portion 35 b the diameter ofwhich becomes larger as the portion is closer to the heating face, andthe whole thereof has a funnel shape. In portions where cooling spotsare easily generated, the solid constituting the substrate is hardlypresent. Instead of it, gas such as air is present.

Accordingly, the heat capacity of the portion where cooling spots areeasily generated gets small. Because of the presence of this portion,portions with low temperature are not easily generated in asemiconductor wafer 59. Since gas such as air accumulates heat andremains in the funnel-shaped portion, the semiconductor wafer 59 can beevenly heated.

In FIG. 10, the through hole 35 has a shape the diameter of whichincreases abruptly at a spot from the vicinity of the heating face(specifically a position whose distance from the heating face of theceramic substrate is ⅔ or less of the thickness of the ceramicsubstrate) toward the heating face. However, the through hole may be athrough hole having such a shape that the diameter thereof increasesgradually from the vicinity of the bottom face side in order to causethe gas (such as the air) having accumulated heat to remain in thevicinity of the heating face.

When this ceramic heater 30 is used to heat the semiconductor wafer 59,it is allowable to receive the semiconductor wafer 59 by means of thelifter pins 36, put the semiconductor wafer 59 on the heating face, andsend electric current to the ceramic heater so as to be heated. It isalso allowable to support the semiconductor wafer 59 in the state thatthe wafer is a given distance apart from the heating face 31 a of theceramic substrate through the lifer pins 36 by holding the lifter pins36 in the state that they project slightly from the heating face 31 a ofthe ceramic substrate 31, and then heat the semiconductor wafer 59.

In particular, when the semiconductor wafer or the like is placed so asto contact the heating face, in general it is easily affected by coolingspots present in the vicinity of the through holes. In the second aspectof the present invention, however, the diameter on the heating face sideof the through holes is larger as described above. Thus, cooling spotsare not easily generated, and thus the semiconductor wafer can be moreevenly heated than that in the prior art.

Before and after the step of using the ceramic substrate of the secondaspect of the present invention to conduct heating treatment and soforth, the semiconductor wafer or the like can be relatively easilyreceived from the previous line or carried to the next line by lettingthe lifter pins 36 pass through the through holes 35 and subsequentlymoving the lifter pins up and down.

When the semiconductor wafer or the like is supported by the lifter pins36, the semiconductor wafer or the like is not rubbed with the ceramicsubstrate. Therefore, no free particles are generated from the ceramicsubstrate.

By arranging a member having projected structures, such as pins and thelike, on the surface of the ceramic substrate, the semiconductor waferor the like can be heated in the state that the semiconductor wafer orthe like is apart from the heating face of the ceramic substrate in thesame manner as in the case of holding the lifter pins in the state thatthe lifter pins project slightly from the heating face of the ceramicsubstrate.

In the ceramic heater according to the second aspect of the presentinvention, the heating elements may be formed inside the ceramicsubstrate or may be formed outside the ceramic substrate.

FIG. 11 is a bottom face view which schematically illustrates anotherexample of the ceramic heater according to the second aspect of thepresent invention. FIG. 12 is a partially enlarged sectional view whichschematically illustrates the ceramic heater in FIG. 11. In this ceramicheater, heating elements are formed on a surface of the ceramicsubstrate.

In the ceramic heater 40, its ceramic substrate 41 is formed in adisk-like form, and heating elements 42 having a concentrically circularpattern are formed on the surface of the ceramic substrate 41. Externalterminals 43, which are terminals for input and output, are connectedthrough a metal covering layer 420 to both ends of the heating element.

In the bottom face of the ceramic substrate 41, bottomed holes 44, forinserting temperature measuring elements (not illustrated) into, areformed.

Additionally, three through holes 45, for letting lifter pins 46 passthrough, are formed in the vicinity of the center of the ceramicsubstrate 41. In the same manner as in the case of the ceramic heater30, the through hole 45 is composed of a columnar portion 45 a and adiameter-increasing portion 45 b. In portions where cooling spots areeasily generated, the solid constituting the substrate is hardlypresent. Accordingly, the heat capacity of the portion where coolingspots are easily generated can be largely lowered. Thus, a semiconductorwafer 59 can be evenly heated.

By letting the lifter pins 46 pass through the through holes 45 and thenmoving the pins up and down, the semiconductor wafer or the like can becarried and moved. By projecting the lifter pins 46 from the heatingface 41 a of the ceramic substrate 41, the semiconductor wafer 59 can beheld in the state that the wafer is apart from the ceramic substrate 41a.

In the ceramic heater according to the second aspect of the presentinvention, the shape of the through holes is not particularly limited ifthe diameter thereof on the heating face side is larger than that on thebottom face. As described, the through holes are preferably composed ofa columnar portion and a diameter-increasing portion as illustrated inFIG. 10.

The number of the through holes formed in the ceramic substrate ispreferably three or more. If the number of the through holes is two orless, it is difficult to support an object to be heated, such as asemiconductor wafer, stably by the lifter pins passed through thethrough holes. The number of the through holes is not particularlylimited if the number is three or more. Since it is also true for thesecond aspect of the present invention that cooling spots are easilygenerated in the through holes portions, it is preferred that the numberthereof is not very large. For example, the number is desirably 11 orless.

The position where the through holes are formed is not particularlylimited. Desirably, the through holes are formed in an area whosedistance from the center of the ceramic substrate is ½ or more of thedistance from the center to the outer edge of the ceramic substrate.This is because this case makes it possible to support a semiconductorwafer or the like more stably. The volume of the peripheral portion islarger than that of the central portion; therefore, if the through holesare formed in the vicinity of the center, the heat capacity of thecentral portion gets small by making the through holes. Thus, thetemperature in the central portion is readily made high. However, if thethrough holes are formed in the peripheral portion, difference in theheat capacity between the central portion and the peripheral portion ishardly generated so that the temperature in the heating face can be madeeven.

The through holes are desirably formed at substantially regularintervals on a single circle having a concentric circle relationshipwith the ceramic substrate since a semiconductor wafer or the like canbe more stably supported and can be still more evenly heated. In thecase that four or more through holes are formed in the ceramicsubstrate, one of the through holes may be formed in the center of theceramic substrate. By the lifter pins, the semiconductor wafer or thelike can be held apart from the ceramic substrate and further thecentral portion of the semiconductor wafer or the like can be preventedform warping when it is heated. As a result, the distance between thesemiconductor wafer or the like and the ceramic substrate is madeconstant so that the semiconductor wafer or the like can be evenlyheated.

When a semiconductor wafer or the like is held apart by the lifter pins,it is desired that the height of the lifter pins projecting from theheating face of the ceramic substrate, the pins being passed through thethrough holes, is from 5 to 5000 μm, that is, that the semiconductorwafer or the like is held from 5 to 5000 μm apart from the heating faceof the ceramic substrate. If the distance is less than 5 μm, thetemperature of the semiconductor or the like is affected by thetemperature distribution in the ceramic substrate and is made uneven. Ifthe distance exceeds 5000 μm, the temperature of the semiconductor waferor the like does not rise easily. In particular, the temperature in theperipheral portion of the semiconductor wafer or the like drops.

An object to be heated and the heating face of the ceramic substrate areseparated from each other more desirably by a distance of 5 to 500 μm,still more desirably 20 to 200 μm.

The diameter of the through holes is desirably from 1 to 100 mm, moredesirably from 1 to 20 mm. In case the through holes have a trapezoidalsectional shape, the diameter of the through holes means the diameterthereof at the position in the middle between the bottom face and theheating face. When the through holes are composed of a columnar portionand a diameter-increasing portion, the diameter thereof means thediameter of the columnar portion. If the diameter of the through holesis less than 1 mm, the lifter pins passed through the through holesbecome too thin so that a semiconductor wafer or the like can not bestably put on the lifter pins with ease. On the other hand, if thediameter of the through holes exceeds 100 mm, the through holes are toolarge so that cooling spots are readily generated in the heating face bythe effect of gas present inside the through holes. Additionally, theheat capacities in a given area of the ceramic substrate are differentbetween the portion where the through holes are present and the portionwhere the through holes are not present; therefore, the temperature inthe heating face readily gets uneven, whereby it is apprehended that thesemiconductor wafer or the like cannot be evenly heated.

The constitutions of parts other than the through holes in the ceramicsubstrate, which are parts of the ceramic heater of the second aspect ofthe present invention, such as temperature measuring elements, heatingelements, and connecting terminals, are the same as in the first aspectof the present invention. Thus, description thereof will not berepeated.

A ceramic body having a cylindrical shape or the like may be bonded tothe bottom face of the ceramic substrate which constitutes the ceramicheater according to the second aspect of the present invention, so as toprotect wires such as external terminals. In this way, the wires such asthe external terminals can be protected from reactive gas, halogen gasand the like.

Furthermore, the ceramic heater according to the second aspect of thepresent invention can be used when a liquid crystal substrate is heated.

The following will describe a process for producing a ceramic heateraccording to the second aspect of the present invention.

Firstly, a ceramic heater wherein heating elements 32 are formed insidea ceramic substrate 31 (see FIGS. 9 and 10) will be described on thebasis of FIG. 13.

(1) Step of Forming the Ceramic Substrate

First, ceramic powder made of a nitride ceramic and the like are mixedwith a binder, a solvent and so on to prepare a paste. This is used toform green sheets 100.

Aluminum nitride and the like can be used as the above-mentioned ceramicpowder made of a nitride ceramic and the like. If necessary, a sinteringaid such as yttria, a compound containing Na or Ca, and the like may beadded thereto.

As the binder, desirable is at least one selected from an acrylic resinbinder, ethylcellulose, butylcellosolve, and polyvinyl alcohol.

As the solvent, desirable is at least one selected from α-terpineol andglycol.

A paste obtained by mixing these is formed into a sheet form by a doctorblade process, to manufacture green sheets.

The thickness of the green sheets is preferably from 0.1 to 5 mm.

(2) Step of Printing a Conductor Containing Paste on the Green Sheet

A metal paste or a conductor containing paste which contains pastecontaining a conductive ceramic, for forming heating elements 32, isprinted on the green sheet 100, so as to form a conductor containingpaste layer 320. A conductor containing paste filled layer 330 forconductor filled through holes 33 a is formed in through holes.

The conductor containing paste contains metal particles or conductiveceramic particles.

The average particle diameter of tungsten particles or molybdenumparticles is preferably from 0.1 to 5 μm. If the average particle isless than 0.1 μm or exceeds 5 μm, the conductor containing paste is noteasily printed.

Such a conductor containing paste may be a composition (paste) obtainedby mixing, for example, 85 to 87 parts by weight of the metal particlesor the conductive ceramic particles; 1.5 to 10 to parts by weight of atleast one binder selected from acrylic resin binders, ethylcellulose,butylcellosolve and polyvinyl alcohol; and 1.5 to 10 parts by weight ofat least one solvent selected from α-terpineol and glycol.

(3) Step of Laminating the Green Sheets

Green sheets 100 on which no conductor containing paste is printed arelaminated on the upper and lower sides of the green sheet 100 on whichthe conductor containing paste is printed (see FIG. 13(a))

At this time, the laminating is performed in such a manner that thegreen sheet 100 on which the conductor containing paste is printed isarranged at a position which has a distance, from the bottom face, of60% or less of the thickness of the laminated green sheets.

Specifically, the number of the green sheets laminated on the upper sideis preferably from 20 to 50, and that of the green sheets laminated onthe lower side is preferably from 5 to 20.

(4) Step of Firing the Green Sheet Lamination

The green sheet lamination is heated and pressed to sinter the greensheets and the inner conductor containing paste. The heating temperatureis preferably from 1000 to2000° C., and the pressing pressure ispreferably from 10 to 20 MPa. The heating is performed in the atmosphereof an inert gas. As the inert gas, argon, nitrogen and the like can beused.

Next, through holes 35, for letting lifter pins 36 for supporting asemiconductor wafer 59 pass through, are formed in the resultantsintered body.

At this time, the through holes 35 having a columnar portion 35 a and adiameter-increasing portion 35 b can be formed by: firstly, formingcolumnar through holes with a drill having an ordinary cutting edge; andsubsequently processing the through hole portions from the heating faceside, by using a drill having a cutting edge capable of making a conicalshaped concave portions. Also, by sandblast treatment, through holeshaving a trapezoidal vertical section, as well as the above-mentionedshaped through holes, can be formed.

The through holes 35 are desirably formed at substantially regularintervals on a single circle having a concentric circle relationshipwith the ceramic substrate 31 for the following reason: the lifter pins36, which are passed through the through holes 35, are widely dispersedon the ceramic substrate 31 and arranged at regular interval; therefore,the semiconductor wafer 59 can be kept more horizontal.

Furthermore, bottomed holes 34, for embedding temperature measuringelements such as thermocouples, are formed in the ceramic substrate (seeFIG. 13(b)). Thereafter, blind holes 33 are provided in order to makethe conductor filled through holes 33 a, which is for connecting theheating elements 32 to external terminals 33, exposed (see FIG. 13(c)).

The above-mentioned steps of making the bottomed holes and the throughholes may be applied to the above-mentioned sheet lamination, but ispreferably applied to the above-mentioned sintered body. This is becausethe lamination may be deformed in the sintering step.

The formation of the through holes and the bottomed holes is usuallyperformed after grinding the surface. Thereafter, the external terminals33 are connected to the conductor filled through holes 33 a forconnecting the inner heating elements 32, and heated for re-flow. Theheating temperature is preferably from 200 to 500° C.

Furthermore, thermocouples (not illustrated) as temperature measuringelements are fitted into the bottomed holes 14 with brazing silver,brazing gold and the like, and then holes are sealed up with aheat-resistant resin such as polyimide, so as to finish the productionof a ceramic heater 30 (see FIG. 13(d)).

The following will describe a process for producing a ceramic heater 40wherein heating elements 42 are formed on the bottom face of a ceramicsubstrate 41 (see FIGS. 11 and 12) on the basis of FIG. 14.

(1) Step of Forming the Ceramic Substrate

A sintering aid such as yttria (Y₂O₃) or B₄C, a compound containing Naor Ca, a binder and so on are blended as appropriate with powder made ofa ceramic such as a nitride ceramic, for example, the above-mentionedaluminum nitride or a carbide ceramic, so as to prepare a slurry.Thereafter, this slurry is made into a granular form by spray drying andthe like. The granules are put into a mold and pressed to be formed intoa plate form or some other form. Thus, a raw formed body (green) isproduced.

Next, this raw formed body is heated and fired to be sintered. Thus, aplate made of the ceramic is produced. Thereafter, the plate is madeinto a given shape to produce the ceramic substrate 41. The shape of theraw formed body may be such a shape that the sintered body can be usedas it is after the firing. By heating and firing the raw formed bodyunder pressure, the ceramic substrate 41 having no pores can beproduced. It is sufficient that the heating and the firing are performedat the sintering temperature or higher. The firing temperature is from1000 to 2500° C. for nitride ceramics or carbide ceramics. The firingtemperature is from 1500 to 2000° C. for oxide ceramics.

Furthermore, the ceramic substrate is drilled so as to form throughholes 45, for letting lifter pins 46 for supporting a semiconductorwafer 59 pass through. The method of forming the through holes is thesame as in the case of the above-mentioned ceramic heater having theheating elements inside.

Additionally, bottomed holes 44, for embedding temperature measuringelements such as thermocouples, are formed in the ceramic substrate (seeFIG. 14(a)).

(2) Step of Printing a Conductor Containing Paste on the CeramicSubstrate

A conductor containing paste is generally a fluid comprising metalparticles, a resin and a solvent, and having a high viscosity. Thisconductor containing paste is printed on portions where heating elements4 are to be formed by screen printing and the like. In this way, aconductor containing paste layer is formed.

The conductor containing paste is desirably formed in such a manner thatsections of the heating elements 42 subjected to the firing arerectangular and flat.

(3) Firing of the Conductor Containing Paste

The conductor containing paste layer printed on the bottom face 41 b ofthe ceramic substrate is heated and fired to remove the resin and thesolvent and sinter the metal particles. Thus, the metal particles arebaked onto the bottom face of the ceramic substrate 41 to form theheating elements 42 (FIG. 14(b)). The heating and firing temperature ispreferably from 500 to 1000° C.

If the above-mentioned oxides are added to the conductor containingpaste, the metal particles, the ceramic substrate and the oxides aresintered to be integrated with each other. Thus, the adhesivenessbetween the heating elements 42 and the ceramic substrate 41 isimproved.

(4) Step of Forming a Metal Covering Layer

Next, a metal covering layer 420 is deposited on the surface of theheating elements (FIG. 14(c)). The metal covering layer 420 can beformed by electroplating, electroless plating, sputtering and the like.From the viewpoint of mass-productivity, electroless plating is optimal.

(5) Fitting of Terminals and so on

A terminal (external terminal 43 for connection to a power source isfitted up to an end of each of the pattern pieces of the heatingelements 42 with solder. Thermocouples (not illustrated) are fixed tothe bottomed holes 44 with brazing silver, brazing gold and the like.The bottomed holes are sealed with a heat-resistant resin such aspolyimide, so as to finish the production of a ceramic heater 40 (FIG.14(d)).

About the ceramic heater of the second aspect of the present invention,electrostatic electrodes are set inside the ceramic substrate, wherebythe ceramic heater can be used as an electrostatic chuck.

By forming a chuck top conductive layer on the surface, the ceramicheater can be used as a ceramic substrate for a wafer prober.

The following will describe a ceramic bonded body according to a thirdaspect of the present invention according to embodiments. The thirdaspect of the present invention is not limited to this description. Inthe following, the ceramic body will be described as a cylindricalceramic body. However, the ceramic body may be a columnar filled body,or may be a triangle polar or square polar hollow body or filled body.

The ceramic bonded body of the third aspect of the present inventionaccording to an embodiment includes: a disk-like ceramic substrateinside which a conductor is provided; and a cylindrical ceramic bodyhaving a cylindrical shape bonded to the bottom face of the ceramicsubstrate, wherein the center of the circle surrounded by the interfacebetween the cylindrical ceramic body and the ceramic substrate is 3 to200 μm apart from the center of the bottom face of the ceramicsubstrate.

FIG. 17(a) is a plan view which schematically illustrates a ceramicbonded body according to the third aspect of the present invention, andFIG. 17(b) is a partially enlarged sectional view which schematicallyillustrates this ceramic bonded body.

FIG. 17 illustrates only a ceramic substrate and the ceramic body in acylindrical form and does not illustrate a conductor formed inside theceramic substrate, or other members.

The ceramic bonded body 1 is formed by bonding the cylindrical ceramicbody 7 to the bottom face of the ceramic substrate 2 having a disk-likeshape. At this time, the face on which the ceramic substrate 2 and thecylindrical ceramic body 7 are bonded is an interface 6.

In the ceramic bonded body 1, the distance L between: the center A ofthe circle surrounded by the interface 6; and the center B of the bottomface of the ceramic substrate 2 is from 3 to 200 μm.

The method for bonding the ceramic substrate and the cylindrical ceramicbody will be described in detail later.

In the case that the ceramic bonded body according to the third aspectof the present invention is applied to a semiconductorproducing/inspecting device, it is desired that a ceramic substratehaving therein conductors is fixed to the upper portion of a supportingcase having a bottom plate and further wires from the conductors arestored in the cylindrical ceramic body bonded to the bottom face of theceramic substrate. This is for preventing the wires from being exposedto corrosive gas and the like and corroded.

In the case that the conductors formed in the ceramic substrateconstituting a ceramic bonded body of the third aspect of the presentinvention are heating elements and conductor circuits, the ceramicbonded body functions as a ceramic heater.

FIG. 18 is a plan view which schematically illustrates a ceramic heaterwhich is an example of the ceramic bonded body of the third aspect ofthe present invention, and FIG. 19 is a sectional view thereof. FIG. 20is a partially enlarged sectional view of the vicinity of thecylindrical ceramic body illustrated in FIG. 19.

As illustrated in FIG. 19, in this ceramic heater 70, cylindricalceramic body 77 is bonded directly to the vicinity of the center of thebottom face 71 b of a ceramic substrate 71 having a disk-like shape. Atthis time, the center of the circle surrounded by the interface betweenthe cylindrical ceramic body 77 and the ceramic substrate 71 is 3 to 200μm apart from the center of the bottom face of the ceramic substrate 71,as described above.

Since the cylindrical ceramic body 77 is formed to adhere closely to thebottom plate (not illustrated) of the supporting case, the inside andthe outside of the cylindrical ceramic body 77 are completely separated.

As illustrated in FIG. 18, heating elements 72 formed of circuits havinga concentrically circular shape are formed in the ceramic substrate 71.About these heating elements 72, two concentric circles adjacent to eachother are connected to each other so as to be a single line as onecircuit.

As illustrated in FIG. 19, conductor circuits 78 extending toward thecenter of the ceramic substrate 71 are formed between the heatingelements 72 and the bottom face 71 b, and ends 72 a of the heatingelement are connected to one end of the conductor circuit 78 through viaholes 86.

The conductor circuit 78 is formed to extend the ends 72 a of theheating element to the central portion. In the ceramic substrate 71, aconductor filled through hole 73′ and a blind hole 79 for making theconductor filled through hole 73′ exposed are formed just under theother end of the conductor circuit 78 extending in the vicinity of theinside of the cylindrical ceramic body 77. This conductor filled throughhole 73′ is connected to an external terminal 83 whose tip has a T-shapethrough a solder layer (not illustrated).

In the case that the ends 72 a of the heating element are inside thecylindrical ceramic body 77, no via holes or conductor circuits arenecessary. Accordingly, the conductor filled through holes 73 aredirectly fitted to the ends of the heating element and they areconnected to the external terminals 83 through a solder layer.

Sockets 85 having a conductive wire 830 are fitted to these externalterminals 83, and this conductive wire 830 is led out from the throughholes formed in the bottom plate (not illustrated) and then connected toa power source (not illustrated) and the like.

On the other hand, temperature measuring elements 84, such asthermocouples, having a lead wire 890 are inserted into the bottomedholes 74 formed in the bottom face 71 b of the ceramic substrate 71, andthe holes are sealed with a heat-resistant resin, a ceramic (such assilica gel and the like. This lead wire 890 is passed through aninsulator (not illustrated), and is led out through a through hole (notillustrated) formed in the bottom plate of the supporting case. Theinside of the insulator is also insulated from the outside thereof.

Furthermore, through holes 75, for letting lifter pins (not illustrated)pass through, are formed in the vicinity of the center of the ceramicsubstrate 71.

The lifter pins can be formed so as to be moved up and down in the statethat an object to be heated, such as a silicon wafer, is put thereon.This makes it possible to deliver the silicon wafer to a non-illustratedcarrying machine or receive the silicon wafer from the carrying machineand further to heat the silicon wafer put on the heating face 71 a ofthe ceramic substrate 71, or support the silicon wafer 50 to 2000 μmapart from the heating face 71 a and heat it.

The silicon wafer may be heated 50 to 2000 μm apart from the heatingface 71 a by making: through holes or concave portions in the ceramicsubstrate 71; inserting supporting pins whose tips are in a spire formor a hemispherical form into the through holes or concave portions;fixing the supporting pins in the state that they project slightly fromthe ceramic substrate 71; and then supporting the silicon wafer by thesupporting piping system.

A coolant introducing pipe and the like may be fitted to the bottomplate of the supporting case. In this case, the temperature of theceramic substrate 71, the cooling rate and so forth can be controlled byintroducing a coolant into this coolant introducing pipe through a pipe.

As described above, in this ceramic heater 70, the cylindrical ceramicbody 77 is bonded to the bottom face 71 b of the ceramic substrate 71and the cylindrical ceramic body 77 is formed to extend to the bottomplate (case wall) of the non-illustrated supporting case; therefore, theinside of the cylindrical ceramic body 77 is completely insulated fromthe outside thereof.

Accordingly, by protecting the conductive wires 830 led out from thethrough holes in the bottom plate by tubular members, even if theceramic heater 70 is surrounded by an atmosphere containing reactivegas, halogen gas and the like, and even in the state that the reactivegas and the like enter easily the inside of the supporting case, thewires inside the cylindrical ceramic body 77 do not corrode. The wires890 from the temperature measuring elements 84 do not corrode since theyare protected from the insulator and so on.

Furthermore, inert gas and the like may be caused to flow slowly in thecylindrical ceramic body 77 so that reactive gas, halogen gas and thelike do not flow in the cylindrical ceramic body 77. In this way, thecorrosion of the conductive wires 830 can be still more surelyprevented.

Since the cylindrical ceramic body 77 has a function for supporting theceramic substrate 71 fixedly, the ceramic substrate 71 can be preventedfrom being warped by its self weight even when the ceramic substrate 71is heated to a high temperature. As a result, an object to be heated,such as a silicon wafer, can be prevented from being damaged, andfurther the object to be heated can be heated to have an eventemperature.

The constitutions of the ceramic substrate and temperature measuringelements which are parts of the ceramic heater of the third aspect ofthe present invention are the same as disclosed in the ceramic heater ofthe first aspect of the present invention. Thus, description thereon isomitted.

The number of the through holes formed to pass the lifter pins throughthe ceramic substrate, and the position where they are formed are notlimited to the above.

The shape of the cylindrical ceramic body in the ceramic bonded body ofthe third aspect of the present invention is a cylindrical shape asillustrated in FIG. 19, and the inner diameter thereof is desirably 30mm or more.

If the diameter is less than 30 mm, the ceramic substrate is not fixedlysupported with ease. When the ceramic substrate is heated to a hightemperature, it is apprehended that the ceramic substrate is warped byits self weight.

The thickness of the cylindrical ceramic body is desirably from 3 to 20mm. If the thickness is less than 3 mm, the thickness of the cylindricalceramic body is too small so that the mechanical strength is poor. Thus,it is apprehended that the cylindrical ceramic body is damaged byrepeating temperature-rising and temperature-dropping thereof. If thethickness exceeds 20 mm, the thickness of the cylindrical ceramic bodyis too large so that the heat capacity gets large. Thus, it isapprehended that the temperature-rising rate drops.

As the ceramic which forms the cylindrical ceramic body, the samematerial for the above-mentioned ceramic substrate can be used. Themethod for bonding the cylindrical ceramic body to the ceramic substratewill be described in detail later.

The constitutions of heating elements, external terminals, conductivewires and so on formed inside the ceramic substrate are the same as inthe ceramic heater of the first aspect of the present invention. Thus,description thereon is omitted.

In the ceramic heater 70 illustrated in FIGS. 18, 19 and 20, the ceramicsubstrate 71 is usually fitted to the upper part of the supporting case(not illustrated). In other embodiments, however, the substrate may beput on the upper face of a supporting face having a substrate-receivingportion at its upper end, and fixed with fixing members such as bolts.

The above-mentioned ceramic heater 70 is desirably used at 100° C. ormore, more desirably 200° C. or more.

The ceramic substrate which constitutes the ceramic bonded body of thethird aspect of the present invention is used to product a semiconductoror inspect a semiconductor. Specifically, examples thereof include anelectrostatic chuck, susceptor, a ceramic heater (hot plate) and thelike.

The above-mentioned ceramic heater is a device wherein only heatingelements are formed inside the ceramic substrate. This makes it possibleto hold an object to be heated, such as a silicon wafer, on the surfaceof the ceramic substrate or apart from the surface, and heat the objectto a given temperature or wash the object.

Furthermore, the ceramic heater which is an example of the ceramicbonded body of the third aspect of the present invention can be usedwhen a liquid crystal substrate is heated.

In the case that conductors formed inside the ceramic substrate whichconstitutes the ceramic bonded body of the third aspect of the presentinvention are electrostatic electrodes or conductor circuits, theceramic bonded body functions as an electrostatic chuck.

FIG. 21 is a vertical sectional view which schematically illustratessuch an electrostatic chuck, and FIG. 22 is a partially enlargedsectional view thereof. FIG. 23 is a horizontal sectional view whichschematically illustrates the vicinity of electrostatic electrodesformed on a substrate which constitutes the electrostatic chuck.

Inside the ceramic substrate 91 which constitutes this electrostaticchuck 90, chuck positive and negative electrostatic layers 92 a and 92 bin a semicircular form are arranged oppositely to each other. A ceramicdielectric film 94 is formed on these electrostatic electrodes. Insidethe ceramic substrate 91, heating elements 920 are formed so that anobject to be heated, such as a silicon wafer, can be heated. Ifnecessary, RF electrodes are embedded in the ceramic substrate 91.

The electrostatic electrodes are preferably made of a metal such as anoble metal (gold, silver, platinum or palladium), lead, tungsten,molybdenum, nickel and the like, or a conductive ceramic such as acarbide of tungsten or molybdenum. These may be used alone or incombination of two or more thereof.

As illustrated in FIGS. 21, 22, in this electrostatic chuck 90,electrostatic electrodes 92 a, 92 b are formed in the ceramic substrate91, and a conductor filled through hole 93 is formed just under an endof each of the electrostatic electrodes 92 a, 92 b. A ceramic dielectricfilm 94 is formed on the electrostatic electrodes 92. Except thesematters, the electrostatic chuck has the same constitution as theabove-mentioned ceramic heater 70.

That is, a cylindrical ceramic body 97 is bonded to the vicinity of thecenter of the bottom face of the ceramic substrate 91. As describedabove, at this time the center of the circle surrounded by the interfacebetween the cylindrical ceramic body 97 and the ceramic substrate 91 is3 to 200 μm apart from the center of the bottom face of the ceramicsubstrate 91.

The conductor filled through holes 93 and conductor filled through holes930 are formed above the area inside of the cylindrical ceramic body 97.These conductor filled through holes 93, 930 are connected to theelectrostatic electrodes 92 a, 92 b and the heating elements 920, andfurther connected to external terminals 960 inserted into blind holes990. A socket 950 having a conductive wire 931 is connected to one endof the external terminal 960. This conductive wire 931 is led out from athrough hole (not illustrated).

In the case of heating elements 920 having an end outside thecylindrical ceramic body 97, via holes 99, conductor circuits 980 andconductor filled through holes 930′ are formed in the same manner as inthe case of the ceramic heater 70 illustrated in FIGS. 18 to 20, wherebyends of the heating elements 920 extend to the inside the cylindricalceramic body 97 (see FIG. 22). Accordingly, by inserting the externalterminals 960 into the blind holes 990 for making the conductor filledthrough holes 930′ exposed and connecting them, the external terminals960 can be stored inside the cylindrical ceramic body 97.

When this electrostatic chuck 90 is worked, voltages are applied to theheating elements 920 and the electrostatic electrodes 92, respectively.In this way, a silicon wafer put on the electrostatic chuck 90 is heatedto a given temperature and further electrostatically absorbed on theceramic substrate 91. This electrostatic chuck may not necessarily havethe heating elements 920.

FIG. 24 is a horizontal sectional view which schematically illustratesanother electrostatic electrode formed on a substrate for electrostaticchuck. A chuck positive electrostatic layer 172, which is composed of asemicircular part 172 a and a combteeth-shaped part 172 b, and a chucknegative electrostatic layer 173, which is also composed of asemicircular part 173 a and a combteeth-shaped part 173 b, are arrangedface-to-face in such a manner that the teeth of one comb teeth shapedpart 172 b extend in staggered relation with the teeth of the other combteeth shaped part 173 b.

FIG. 25 is a horizontal sectional view which schematically illustratesfurther another electrostatic electrode formed on a substrate for anelectrostatic chuck. In this electrostatic chuck, chuck positiveelectrostatic layers 182 a, 182 b and chuck negative electrostaticlayers 183 a, 183 b, each of which has a shape obtained by dividing acircle into 4 parts, are formed inside the ceramic substrate 181. Thetwo chuck positive electrostatic layers 182 a, 182 b and the two chucknegative electrostatic layers 183 a, 183 b are formed to cross eachother.

In the case that electrodes having a form obtained by dividing anelectrode having a circular shape or some other shape are formed, thenumber of divided pieces is not particularly limited and may be 5 ormore. Its shape is not limited to a fan-shape.

The following will describe a process for producing a ceramic heater, asan example of a process for producing the ceramic bonded body of thethird aspect of the present invention, referring to FIG. 26.

FIGS. 26(a) to (d) are sectional views which schematically illustratesome parts of the process for producing a ceramic heater, which is anexample of the ceramic bonded body of the third aspect of the presentinvention.

(1) Step of Forming Green Sheets

First, a green sheet 500 is formed in the same way as in the process forproducing the ceramic heater of the first aspect of the presentinvention.

Next, the following are produced: a green sheet wherein portions 860which will be via holes for connecting an end of a heating element to aconductor circuit are formed; and a green sheet wherein portions 730,730′ which will be conductor filled through hole for connecting theconductor circuit to an external terminal are formed.

If necessary, the following are formed: portions which will be throughholes for letting lifter pins for carrying a silicon wafer pass through;portions which will be through holes for inserting supporting pins forsupporting a silicon wafer into; portions which will be bottomed holesfor embedding temperature measuring elements such as thermocouples; andthe like. About the through holes and the bottomed holes, theabove-mentioned working may be performed after a green sheet laminationwhich will be described later is formed, or after the lamination isformed and fired.

The above-mentioned paste to which carbon is added may be filled intothe portions 860, which will be the via holes, and the portions 730,730′, which will be the conductor filled through holes. This is becausethe carbon in the green sheet reacts with tungsten or molybdenum filledinto the conductor filled through holes to form carbides thereof.

(2) Step of Printing a Conductor Containing Paste on the Green Sheet

A metal paste or a conductor containing paste which contains aconductive ceramic is printed on the green sheet wherein the portions860, which will be the via holes, are formed, so as to form a conductorcontaining paste layer 720.

The conductor containing paste contains metal particles or conductiveceramic particles.

The average particle diameter of tungsten particles or molybdenumparticles, which will be the metal particles, is preferably from 0.1 to5 μm. If the average particle is less than 0.1 μm or exceeds 5 μm, theconductor containing paste is not easily printed.

Such a conductor containing paste may be a composition (paste) obtainedby mixing, for example, 85 to 87 parts by weight of the metal particlesor the conductive ceramic particles; 1.5 to 10 to parts by weight of atleast one binder selected from acrylic resin binders, ethylcellulose,butylcellosolve and polyvinyl alcohol; and 1.5 to 10 parts by weight ofat least one solvent selected from α-terpineol and glycol.

A conductor containing paste which is usually used when electrostaticelectrodes and the like are formed is printed on the green sheet whereinthe portions 730, 730′, which will be the conductor filled throughholes, are formed, so as to form a conductor containing paste layer 780.

(3) Step of Laminating the Green Sheets

Green sheets 500 on which no conductor containing paste is printed arelaminated on the green sheet on which the conductor containing paste isprinted, and then the green sheet wherein the conductor containing pastelayer 780 is formed is put beneath the resultant. Furthermore, greensheets 500 wherein no conductor containing paste layer is printed isprinted are laminated beneath this green sheet (see FIG. 26(a)).

At this time, the number of the green sheets 500 laminated on the upperside of the green sheet wherein the conductor containing paste layer 720is printed is made larger than that of the green sheets 500 laminated onthe lower side, so that the positions where heating elements to beproduced are formed are biased toward the bottom side.

Specifically, the number of the green sheets 500 laminated on the upperside is preferably from 20 to 50, and that of the green sheets 500laminated on the lower side is preferably from 5 to 20.

(4) Step of Firing the Green Sheet Lamination

The green sheet lamination is heated and pressed to sinter the greensheets 500 and the inner conductor containing paste layers 720, 780, andso forth, thereby producing a ceramic substrate 71, heating elements 72,conductor circuits 78, and so forth (see FIG. 26(b)).

The heating temperature is preferably from 1000 to 2000° C., and thepressing pressure is preferably from 10 to 20 MPa. The heating isperformed in the atmosphere of an inert gas. As the inert gas, argon,nitrogen and the like can be used.

Next, bottomed holes, for embedding temperature measuring elements, areformed in the bottom face 71 b of the ceramic substrate 71 (notillustrated). The bottomed holes can be formed by grinding the surfaceand then performing drilling or blast treatment such as sandblast. Theabove-mentioned bottomed holes or concave portions may be formed afterthe ceramic substrate 71 and a cylindrical ceramic body 70, which willbe described later, are bonded to each other, or may be formed at thesame time of laminating and firing the green sheets 500 after portionswhich will be the bottomed holes are beforehand formed in the greensheets 500.

Blind holes 79 are also provided to make the conductor filled throughholes 73, 73′, for connecting the inner heating elements 72, exposed.The blind holes 79 may also be formed after the ceramic substrate 71 isbonded to the cylindrical ceramic body 77.

(5) Production of the Cylindrical Ceramic Body

Nitride aluminum power and the like are put into a cylindrical mold, andis formed. If necessary, the formed body is cut. This is sintered at aheating temperature of 1000 to 2000° C. under a normal pressure toproduce the cylindrical ceramic body 77. The sintering is performed inan inert gas atmosphere. Examples of the inert gas which can be usedinclude argon and nitrogen.

The size of the cylindrical ceramic body 77 is adjusted in such a mannerthat the conductor filled through holes 73, 73′ formed inside theceramic substrate are put in the body 77.

Next, end faces of the cylindrical ceramic body 77 are ground to be madeflat.

(6) Bonding of the Ceramic Substrate to the Cylindrical Ceramic Body

In the state that the central vicinity of the bottom face 71 b of theceramic substrate 71 contacts the end face of the cylindrical ceramicbody 77, the ceramic substrate 71 and the cylindrical ceramic body 77are heated and bonded to each other. At this time, the conductor filledthrough holes 73, 73′ inside the ceramic substrate 71 are allowed to beabove an area inside the inner diameter of the cylindrical ceramic body77, and further the center of the circle surrounded by the interfacebetween the cylindrical ceramic body 77 and the ceramic substrate 71 ispositioned 3 to 200 μm apart from the center of the bottom face of theceramic substrate 71 to bond the cylindrical ceramic body 77 to thebottom face 71 b of the ceramic substrate 71 (see FIG. 26(c)).

Specifically, a mask 190 in which an opening 191 is formed asillustrated in FIG. 27 is put on the bottom face of the ceramicsubstrate 71 and subsequently the cylindrical ceramic body 77 is fittedinto the opening 191 and heated, thereby bonding the ceramic substrate71 and the cylindrical ceramic body 77 to each other.

Since the opening diameter of the opening 191 is equal to the outerdiameter of the cylindrical ceramic body 77, the distance between thecenter C of the opening 191 and the center B of the bottom face of theceramic substrate 71 is equal to the distance L between: the center ofthe circle surrounded by the interface between the ceramic substrate 71and the cylindrical ceramic body 77; and the center of the bottom faceof the ceramic substrate 71.

As the method of bonding the ceramic substrate 71 to the cylindricalceramic body 77, a method of using brazing gold, brazing silver and thelike to perform brazing, a method of using an adhesive made ofoxide-based glass and the like to bond them, or some other method can beused.

The ceramic substrate 71 and the cylindrical ceramic body 77 can also bebonded to each other by a method of applying a ceramic paste comprisingthe same main component as the ceramic which constitutes the ceramicsubstrate 71 and the cylindrical ceramic body 77, and then sinteringthis, or a method of applying a solution containing a sintering aid tobonding faces of the ceramic substrate and the cylindrical ceramic body.

In the third aspect of the present invention, thermal stress in thebonding faces can be dispersed even if any one of the bonding methods isused. Therefore, the air-tightness of the bonded portions of the ceramicsubstrate 71 and the cylindrical ceramic body 77 can be ensured.

(7) Fitting of Terminals and so on

External terminals 83 are inserted into the blind holes 79 formed insidethe inner diameter of the cylindrical ceramic body 77 through a solderor a brazing material, and the solder and the like are heated forre-flow, thereby connecting the external terminals 83 to the conductorfilled through holes 73, 73′ (FIG. 26(d)).

The heating temperature is preferably from 90 to 450° C. in the case ofthe solder treatment, and is preferably from 900 to 1100° C. in the caseof the treatment with the brazing material.

Next, the external terminals 83 are connected through sockets 85 toconductive wires 830 connected to a power source (see FIG. 19).

Furthermore, thermocouples as temperature measuring elements areinserted into the formed bottomed holes, and the holes are sealed with aheat-resistant resin and the like, whereby a ceramic heater having thecylindrical ceramic body on the bottom face thereof can be produced.

According to this ceramic heater, after a semiconductor wafer such as asilicon wafer is put on the ceramic heater or the silicon wafer or thelike is held by lifter pins, supporting pins or some other member, anoperation such as washing can be performed while the silicon wafer orthe like is heated or cooled.

An electrostatic chuck can be produced by forming electrostaticelectrodes inside the ceramic substrate when the above-mentioned ceramicheater is produced. In this case, however, it is necessary to formconductor filled through holes for connecting the electrostaticelectrodes and external terminals, but it is unnecessary to form throughholes for inserting supporting pins.

In the case that electrodes are formed inside the ceramic substrate, itis advisable that a conductor containing paste layer which will beelectrostatic electrodes is formed on the surface of a green sheet inthe same manner as in the case of forming heating elements.

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention will be described in more detail by way of workingexamples hereinafter.

EXAMPLE 1 Production of Ceramic Heater (See FIGS. 1, 2 and 5)

(1) The following paste was used to perform formation by a doctor blademethod, so as to form a green sheet 50 having a thickness of 0.47 μm: apaste obtained by mixing 100 parts by weight of aluminum nitride powder(manufactured by Tokuyama Corp., average particle diameter: 0.6 μm), 4parts by weight of alumina, 11.5 parts by weight of an acrylic resinbinder, 0.5 part by weight of a dispersant and 53 parts by weight ofalcohols of 1-butanol and ethanol.

(2) Next, this green sheet 50 was dried at 80° C. for 5 hours, andsubsequently portions which would be conductor filled through holes 13 awere formed by punching.

(3) The following were mixed to prepare a conductor containing paste A:100 parts by weight of tungsten carbide particles having an averageparticle diameter of 1 μm, 3.0 parts by weight of an acrylic resinbinder, 3.5 parts by weight of α-terpineol solvent, and 0.3 part byweight of a dispersant.

The following were mixed to prepare a conductor containing paste B: 100parts by weight of tungsten particles having an average particlediameter of 3 μm, 1.9 parts by weight of an acrylic resin binder, 3.7parts by weight of α-terpineol solvent, and 0.2 part by weight of adispersant.

This conductor containing paste A was printed on the green sheet byscreen printing, so as to form a conductor containing paste layer 120for heating elements. The printed pattern was made into a concentricallycircular pattern as described in FIG. 1.

Moreover, the conductor containing paste B was filled into the portionswhich would be conductor filled through holes 13 a for connection toexternal terminals 13, so as to form a filled layer 130.

Thirty seven green sheets 50 on which no conductor containing paste wasprinted were laminated on the upper side (heating surface) of the greensheet 50 that had been subjected to the above-mentioned processing, andthe same thirteen green sheets were laminated on the lower side of thegreen sheet 50. The resultant was pressed at 130° C. and a pressure of 8MPa to form a lamination (see FIG. 5(a)).

(4) Next, the resultant lamination was degreased at 600° C. in theatmosphere of nitrogen gas for 5 hours and hot-pressed at 1890° C. and apressure of 15 MPa for 10 hours to yield a ceramic plate 3 mm inthickness. This was cut off into a disk 210 mm in diameter to prepare aceramic plate having therein heating elements 12 having a thickness of 6μm and a width of 10 mm.

(5) Next, the ceramic plate obtained in the (4) was ground with adiamond grindstone. Subsequently, bottomed holes 14, for insertingthermocouples into, were formed in the bottom face.

Moreover, three through holes 15 (diameter: 5.6 mm), for letting lifterpins (diameter: 5 mm) for carrying a semiconductor wafer or the likepass through, were formed (see FIG. 5(b)).

The through holes 15 were formed at regular intervals on a circle havinga diameter of 116 mm and having a concentric circle relationship withthe ceramic substrate 11.

The through holes 15 were present in an area whose distance from thecenter of the ceramic substrate 11 was 55%, that is, ½ or more of thedistance from the center to the outer edge thereof.

(6) Next, the portions above the formed conductor filled through holes13 a were hollowed out to form blind holes 3 b (see FIG. 5(c)). Brazinggold made of Ni and Au was used and heated for re-flow to connectexternal terminals 13 made of kovar to the blind holes 13 b (see FIG.5(d)).

(7) Thermocouples (not illustrated) for temperature-control wereembedded in the bottomed holes 14 to finish the production of a ceramicheater 10 of the first aspect of the present invention.

EXAMPLE 2 Production of Ceramic Heater (See FIGS. 3, 4 and 6)

(1) A composition made of 100 parts by weight of aluminum nitride powder(average particle diameter: 0.6 μm), 4 parts by weight of yttria(average particle diameter: 0.4 μm), 12 parts by weight of an acrylicresin binder and an alcohol was subjected to spray-drying to formgranular powder.

(2) Next, this granular powder was put into a mold and formed into aflat plate form to obtain a raw formed body (green).

(3) next, this raw formed body was hot-pressed at 1800° C. and apressure of 20 MPa to yield a nitride aluminum plate having a thicknessof 3 mm.

Next, this plate was cut out into a disk having a diameter of 210 mm, soas to prepare a plate made of the ceramic (ceramic substrate 21). Thisceramic substrate 21 was drilled to form three through holes 25(diameter: 3.5 mm), for passing lifter pins 26 (diameter: 3 mm) through,and bottomed holes 24 for embedding thermocouples (see FIG. 6(a)).

The through holes 25 were formed at regular intervals on a circle havinga concentric circle relationship with the ceramic substrate 21 andhaving a diameter of 158 mm.

The positions where the through holes 25 were formed were positionswhose distance from the center of the ceramic substrate 21 was 75%, thatis, ½ or more of the distance from the center to the outer edge thereof.

(4) A conductor containing paste layer was formed on the ceramicsubstrate 21 obtained in the above-mentioned step (3) by screenprinting. The printed pattern was a concentrically circular patternillustrated in FIG. 3.

The used conductor containing paste was a paste having a composition of48% by weight of Ag, 21% by weight of Pt, 1.0% by weight of SiO₂, 1.2%by weight of B₂O₃, 4.1% by weight of ZnO, 3.4% by weight of PbO, 3.4% byweight of ethyl acetate and 17.9% by weight of butyl carbitol.

The conductor containing paste was a Ag-Pt paste, and the silverparticles had an average particle diameter of 4.5 μm, and were scaly.The Pt particles had an average particle size of 0.5 μm, and werespherical.

(5) Furthermore, the ceramic substrate 21 was heated and fired at 780°C. after the formation of the conductor containing paste layer, so as tosinter Ag and Pt in the conductor containing paste and bake them ontothe ceramic substrate 21. Thus, heating elements 22 were formed (seeFIG. 6(b)). The heating elements 22 had a thickness of 5 μm, a width of2.4 mm and an area resistivity of 7.7 mΩ/□.

(6) The ceramic substrate 21 manufactured in the above-mentioned (5) wasimmersed into an electroless nickel plating bath consisting of anaqueous solution containing 80 g/L of nickel sulfate, 24 g/L of sodiumhypophosphite, 12 g/L of sodium acetate, 8 g/L of boric acid, and 6 g/Lof ammonium chloride to precipitate a metal covering layer (nickellayer) 220 having a thickness of 1 μm on the surface of the silver-leadheating elements 22 (see FIG. 6(c)).

(7) Next, by screen printing, a silver-lead solder paste (manufacturedby Tanaka Kikinzoku Kogyo K.K.) was printed on portions onto whichterminal portions 23 for attaining connection to a power source would beset up, to form a solder layer (not illustrated).

Next, the external terminals 23 made of kovar were put on the solderlayer, and heated for re-flow at 420° C. to attach the externalterminals 23 onto the surface of the heating elements 22 (see FIG.6(d)).

(8) Thermocouples (not illustrated) for temperature-control were sealedin the bottomed holes 24 with a polyimide to finish the production of aceramic heater 20 of the first aspect of the present invention.

EXAMPLE 3

(1) The following paste was used to perform formation by a doctor blademethod, so as to form a green sheet 50 having a thickness of 0.47 μm: apaste obtained by mixing 100 parts by weight of SiC powder (manufacturedby Yakushima Denko, average particle diameter: 1.1 μm), 4 parts byweight of B₄C, 11.5 parts by weight of an acrylic resin binder, 0.5 partby weight of a dispersant and 53 parts by weight of alcohols of1-butanol and ethanol. Furthermore, 80 parts by weight of borosilicateglass having an average particle size of 1.0 μm, 5 parts by weight ofpolyethylene glycol and 15 parts by weight of alcohol were mixed toyield a glass paste. This glass paste was applied to the formed greensheet.

(2) Next, this green sheet was dried at 80° C. for 5 hours, andsubsequently portions which would be conductor filled through holes wereformed by punching.

(3) The following were mixed to prepare a conductor containing paste A:100 parts by weight of tungsten carbide particles having an averageparticle diameter of 1 μm, 3.0 parts by weight of an acrylic typebinder, 3.5 parts by weight of α-terpineol solvent, and 0.3 part byweight of a dispersant.

The following were mixed to prepare a conductor containing paste B: 100parts by weight of tungsten particles having an average particlediameter of 3 μm, 1.9 parts by weight of an acrylic resin binder, 3.7parts by weight of α-terpineol solvent, and 0.2 part by weight of adispersant.

This conductor containing paste A was printed on the green sheet byscreen printing, so as to form a conductor containing paste layer forheating elements. The printed pattern was formed into a concentricallycircular pattern as described in FIG. 3.

Moreover, the conductor containing paste B was filled into the portionswhich would be the conductor filled through holes for connection toexternal terminals, so as to form a filled layer.

The glass paste was applied to the green sheet which had been subjectedto the above-mentioned processing, and further thirty seven green sheetson which no conductor containing paste was printed were laminated on theupper side (heating surface) of the green sheet, and the same thirteengreen sheets were laminated on the lower side of the green sheet. Theresultant was pressed at 130° C. and a pressure of 8 MPa to form alamination.

(4) Next, the resultant lamination was degreased at 600° C. in theatmosphere of nitrogen gas for 5 hours and hot-pressed at 1890° C. and apressure of 15 MPa for 10 hours to yield a ceramic plate 3 mm inthickness. This was cut off into a disk 230 mm in diameter to prepare aceramic plate having therein heating elements having a thickness of 6 μmand a width of 10 mm. Furthermore, three through holes for lifter pins,which had a diameter of 5 mm, were formed at regular intervals on acircle having a diameter of 207 mm and having a concentric circlerelationship with the ceramic substrate. The positions where the throughholes were formed were present in an area whose distance from the centerof the ceramic substrate was 90%, that is, ½ or more of the distancefrom the center to the outer edge thereof.

(5) Next, the ceramic plate obtained in the (4) was ground with adiamond grindstone. Furthermore, a sputtering machine (ASP-34,manufactured by Showa Sinku) was used to form a magnesium fluoride filmhaving a thickness of 2 mm on the surface.

(6) Next, the portions above the formed conductor filled through holes13 a were hollowed out to form blind holes. Brazing gold made of Ni andAu was used and heated for re-flow to connect external terminals made ofkovar to the blind holes.

(7) Thermocouples (not illustrated) for temperature-control wereembedded in the bottomed holes to yield a ceramic heater.

TEST EXAMPLE 1

This example was basically the same as in Example 1, but the diameterwas set to 330 mm, and the positions of the through holes for lifterpins were at positions whose distance from the center of the ceramicsubstrate was 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% of thedistance from the center to the outer edge thereof. As will be describedlater, the temperature evenness in the heating face when the temperatureof the ceramic heater was risen and the number of free particles weremeasured.

COMPARATIVE EXAMPLE 1 Production of Ceramic Heater

A ceramic heater was produced in the same way as in Example 1 exceptthat through holes (diameter: 5.6 mm) , for letting lifter pins(diameter: 5.0 mm) pass through, were formed at positions describedbelow.

That is, three through holes were formed at regular intervals on acircle having a diameter of 63 mm and having a concentric circlerelationship with the ceramic substrate.

The positions where the through holes were formed were positions whosedistance from the center of the ceramic substrate was 30% of thedistance from the center to the outer edge thereof, and were not in anarea whose distance from the center was ½ or more thereof.

A silicon wafer was placed by means of the lifter pins at each ofceramic heaters according to Examples 1 to 3 and Comparative Example 1,and electric current was sent thereto so as to rise the temperaturethereof to 300° C. They were evaluated by the following methods. Theresults are shown in Table 1.

The nine ceramic heaters according to Test Example were also evaluatedby the following methods. The results are shown in FIGS. 7 and 8.

The lifter pins projected by 50 μm from the heating face of the ceramicheater. The portions of the silicon wafer supported by the lifter pinswere 50 μm apart from the heating face.

Evaluation Method

(1) Temperature Evenness of the In-face Temperature of the Heating Faceat the Time of Rising the Temperature

The temperature of the ceramic heater was risen to 300° C. in 45 secondswhile a silicon wafer having thermocouples was placed. The difference inthe temperature of the silicone wafer between the highest temperatureand the lowest temperature in the step of rising the temperature wasexamined.

(2) The Number of Free Particles

A semiconductor wafer having a diameter of 200 mm or 300 mm was placed,and a test wherein this semiconductor wafer was pushed up by the lifterpins was carried out 100 times. The number of free particles adhering tothe wafer was then measured. In the free particle-number measurement,arbitrary 10 points were observed with an electron microscope to measurethe number of free particles, and the number was converted to the numberper cm². TABLE 1 In-face temperature distribution in the heating face atthe time of Distance of the rising the The number of through holestemperature free particles from the center (%) *1 (° C.) *2 (pcs/cm²)Example 1 55 2 68 Example 2 75 1.5 53 Example 3 90 1.8 96 Comparative 305 265 Example 1*1) Distance of the through holes from the center: Percentage of thedistance from the center of the ceramic substrate to the through holesto the distance from the center to the outer edge of the ceramicsubstrate*2) In face temperature distribution (° C.) in the heating face: Maximumof the temperature difference between the highest temperature and thelowest temperature in the heating face at stationary time

As is evident from Table 1, the temperature of the ceramic heatersaccording to the Examples was even at the time of rising thetemperature. On the other hand, the temperature of the ceramic heateraccording to the comparative example was largely dispersed at the timeof rising the temperature. This is because: in the ceramic heateraccording to the comparative example, the three through holesconcentrated to the central portion thereof and the heat capacity perunit area (volume) of the central portion became smaller; therefore, thetemperature of the central portion easily got high when the temperaturewas risen. On the other hand, in the ceramic heaters according to theExamples, this is also presumed to be because, the heat capacities perunit area (volume) between the central portion and the peripheralportion were hardly different since the through holes were formed in theperipheral portion, which had a large area (large volume).

It is understood from FIG. 7 that for the above-mentioned reason thetemperature was even at the time of rising the temperature in the casethat the through holes were formed at positions whose distance from thecenter of the ceramic substrate was 50% or more of the distance from thecenter to the outer edge thereof.

It can be understood from FIG. 8 that the number of free particles gotfewer in the case that the through holes were formed at positions whosedistance from the center of the ceramic substrate was 50% or more of thedistance from the center to the outer edge thereof. As described above,it is presumed that: when the wafer warped upwards into a convex form,the outer circumference contacted the ceramic substrate linearly andscratched the ceramic substrate surface, whereby free particles weregenerated; however, in the first aspect of the present invention, thepositions of the through holes for the lifter pins were arranged in anarea whose distance from the center was ½ or more of the distancebetween the outer edge and the center of the substrate, whereby freeparticles were prevented from being generated.

EXAMPLE 4 Production of Ceramic Heater (See FIGS. 9, 10 and 13)

(1) The following paste was used to perform formation by a doctor blademethod, so as to form a green sheet 100 having a thickness of 0.47 μm: apaste obtained by mixing 100 parts by weight of aluminum nitride powder(manufactured by Tokuyama Corp., average particle diameter: 0.6 μm), 4parts by weight of alumina, 11.5 parts by weight of an acrylic resinbinder, 0.5 part by weight of a dispersant and 53 parts by weight ofalcohols of 1-butanol and ethanol.

(2) Next, this green sheet 100 was dried at 80° C. for 5 hours, andsubsequently portions which would be conductor filled through holes 33 awere formed by punching.

(3) The following were mixed to prepare a conductor containing paste A:100 parts by weight of tungsten carbide particles having an averageparticle diameter of 1 μm, 3.0 parts by weight of an acrylic resinbinder, 3.5 parts by weight of α-terpineol solvent, and 0.3 part byweight of a dispersant.

The following were mixed to prepare a conductor containing paste B: 100parts by weight of tungsten particles having an average particlediameter of 3 μm, 1.9 parts by weight of an acrylic resin binder, 3.7parts by weight of α-terpineol solvent, and 0.2 part by weight of adispersant.

This conductor containing paste A was printed on the green sheet byscreen printing, so as to form a conductor containing paste layer 320for heating elements. The printed pattern was formed into aconcentrically circular pattern as described in FIG. 9.

Moreover, the conductor containing paste B was filled into the portionswhich would be conductor filled through holes 33 a for connection toexternal terminals 33, so as to form a filled layer 330.

Thirty seven green sheets 100 on which no conductor containing paste wasprinted were laminated on the upper side (heating surface) of the greensheet 100 that had been subjected to the above-mentioned processing, andthe same thirteen green sheets were laminated on the lower side thereof.The resultant was pressed at 130° C. and a pressure of 8 MPa to form alamination (see FIG. 13(a)).

(4) Next, the resultant lamination was degreased at 600° C. in theatmosphere of nitrogen gas for 5 hours and hot-pressed at 1890° C. and apressure of 15 MPa for 10 hours to yield a ceramic plate 4 mm inthickness. This was cut off into a disk of 310 mm in diameter to preparea ceramic plate having therein heating elements 32 having a thickness of6 μm and a width of 10 mm.

(5) Next, the ceramic plate obtained in the (4) was ground with adiamond grindstone. Subsequently bottomed holes 34, for insertingthermocouples into, were formed in the bottom face.

Moreover, three through holes 35, for letting lifter pins 36 (diameter:3 mm) for carrying a semiconductor wafer or the like pass through, wereformed (see FIG. 13(b)).

About the through holes 35, the diameter of their columnar portion 35 awas 3.5 mm and the length thereof was 2 mm, and depth (length) of theirdiameter-increasing portion 35 b was 2 mm and the diameter, at theheating face, of the diameter-increasing portion 35 b was 7 mm (see FIG.10).

The through holes 35 were formed at regular intervals on a circle havinga diameter of 200 mm and having a concentric circle relationship withthe ceramic substrate 31.

(6) Next, the portions above the formed conductor filled through holes33 a were hollowed out to form blind holes 33 b (see FIG. 13(c)).Brazing gold made of Ni and Au was used and heated for re-flow toconnect external terminals 33 made of kovar to the blind holes 33 b (seeFIG. 13(d)).

(7) Thermocouples (not illustrated) for temperature-control wereembedded in the bottomed holes 34 to finish the production of a ceramicheater 30 of the second aspect of the present invention.

EXAMPLE 5 Production of Ceramic Heater (See FIGS. 11, 12 and 14)

(1) A composition made of 100 parts by weight of aluminum nitride powder(average particle diameter: 0.6μm), 4parts by weight of yttria (averageparticle diameter: 0.4 μm), 12 parts by weight of an acrylic resinbinder and an alcohol was subjected to spray-drying to form granularpowder.

(2) Next, this granular powder was put into a mold and formed into aflat plate form to obtain a raw formed body (green).

(3) Next, this raw formed body was hot-pressed at 1800° C. and apressure of 20 MPa to yield a nitride aluminum plate having a thicknessof 5 mm.

Next, this plate was cut out into a disk having a diameter of 310 mm, soas to prepare a plate made of the ceramic (ceramic substrate 41). Thisceramic substrate 41 was drilled to form three through holes 45(diameter: 3.5 mm), for letting lifter pins 46 (diameter: 3 mm) passthrough, and bottomed holes 44 for embedding thermocouples (see FIG.14(a)).

About the through holes 45, the diameter of their columnar portion 45 awas 3.5 mm and the length thereof was 3 mm, and the depth (length) oftheir diameter-increasing portion 45 b was 2 mm and the diameter, in theheating face, of the diameter-increasing portion 45 b was 10 mm (seeFIG. 12).

The through holes 45 were formed at regular intervals on a circle havinga concentric circle relationship with the ceramic substrate 41 andhaving a diameter of 40 mm.

(4) A conductor containing paste layer was formed on the ceramicsubstrate 41 obtained in the above-mentioned (3) by screen printing. Theprinted pattern was a concentrically circular pattern illustrated inFIG. 3.

The used conductor containing paste was a paste having a composition of48% by weight of Ag, 21% by weight of Pt, 1.0% by weight of SiO₂, 1.2%by weight of B₂O₃, 4.1% by weight of ZnO, 3.4% by weight of PbO, 3.4% byweight of ethyl acetate and 17.9% by weight of butyl carbitol.

This conductor containing paste was a Ag-Pt paste, and the silverparticles had an average particle diameter of 4.5 μm, and were scaly.The Pt particles had an average particle size of 0.5 μm, and werespherical.

(5) Furthermore, the ceramic substrate 41 was heated and fired at 780°C. after the formation of the conductor containing paste layer, so as tosinter Ag and Pt in the conductor containing paste and bake them ontothe ceramic substrate 41. Thus, heating elements 42 were formed (seeFIG. 14(b)). The heating elements 42 had a thickness of 5 μm, a width of2.4 mm and an area resistivity of 7.7 mΩ/□.

(6) The ceramic substrate 41 formed in the above-mentioned (5) wasimmersed into an electroless nickel plating bath consisting of anaqueous solution containing 80 g/L of nickel sulfate, 24 g/L of sodiumhypophosphite, 12 g/L of sodium acetate, 8 g/L of boric acid, and 6 g/Lof ammonium chloride to precipitate a metal covering layer (nickellayer) 420 having a thickness of 1 μm on the surface of the silver-leadheating elements 42 (see FIG. 14(c)).

(7) By screen printing, a silver-lead solder paste (manufactured byTanaka Kikinzoku Kogyo K. K.) was printed on portions onto whichterminal portions 43 for attaining connection to a power source would beset up, to form a solder layer (not illustrated).

Next, the external terminals 43 made of kovar were put on the solderlayer, and heated for re-flow at 420° C. to attach the externalterminals 43 onto the surface of the heating elements 42 (see FIG.14(d)).

(8) Thermocouples (not illustrated) for temperature-control were sealedin the bottomed holes 44 with a polyimide to finish the production of aceramic heater 40 of the second aspect of the present invention.

COMPARATIVE EXAMPLE 2 Production of Ceramic Heater

In the same way as in the prior art, a ceramic heater was produced inthe same way as in Example 4 except that columnar through holes(diameter: 3.5 mm), for letting lifter pins (diameter: 3.0 mm) passthrough, were formed in the ceramic substrate.

COMPARATIVE EXAMPLE 3

A ceramic heater was produced in the same way as in Example 4 exceptthat plugs, which were capable of being fitted into the through holesand were made of AlN, were fitted to the through holes.

A silicon wafer was placed by means of the lifter pins at each ofceramic heaters according to Examples 4 and 5 and Comparative Examples 2and 3, and electric current was sent thereto so as to rise thetemperature thereof to 300° C. They were evaluated by the followingmethods.

The lifter pins projected by 50 μm from the heating face of the ceramicheater. The portions of the silicon wafer which is supported by thelifter pins were 50 μm apart from the heating face.

Evaluation Method

(1)Temperature Evenness of the In-Face Temperature of the Heating Faceat the Time of Rising the Temperature

The temperature of the ceramic heater was risen to 300° C. in 45 secondswhile a silicon wafer having thermocouples was placed. The difference inthe temperature of the silicone wafer between the highest temperatureand the lowest temperature in the step of rising the temperature wasexamined. The results are shown in Table 2.

(2) The Number of Free Particles on the Silicon Wafer

The temperature of the ceramic heater was risen to 300° C. Thereafter,the number of free particles generated on the silicon wafer wasmeasured. The results are shown in Table 2. TABLE 2 In face-temperaturedistribution in the heating face The number of at the time of risingfree particles the temperature (° C.) (pcs/cm²) Example 4 3 30 Example 52 30 Comparative Example 2 5 30 Comparative Example 3 2 500Note)In face-temperature distribution: difference between the highesttemperature and the lowest temperature in the silicon wafer

As is evident from Table 2, according to the ceramic heaters accordingto the Examples, the temperature of the silicon wafer was even at thetime of rising the temperature. On the other hand, according to theceramic heater according to Comparative Example 2, the temperature ofthe silicon wafer was largely dispersed at the time of rising thetemperature. In particular, at portions corresponding to the portionswhere the through holes were formed, the temperature thereof dropped. Itappears that the reason for this is as follows: in the ceramic heateraccording to Comparative Example 2, the heat capacity of cooling spotportions was large since the through holes had a columnar shape and thediameter thereof was not increased in the vicinity of the heating face,and this resulted in a drop in the temperature of silicon wafer atportions corresponding to the portions where the through holes wereformed.

On the other hand, in the ceramic heaters of the Examples, the throughholes were composed of the columnar portion and the diameter-increasingportion and the diameter thereof was increased in the vicinity of theheating face; therefore, the heat capacity of portions where coolingspots were easily generated was small. For this reason, a dispersion inthe temperature of the silicon wafer is considered not be easilygenerated.

In the ceramic heater according to Comparative Example 3, the plugs madeof AlN were fitted to the through holes. Thus, the ceramic heater had noportions where cooling spots were easily generated. For this reason, thetemperature of the silicon wafer was even at the time of rising thetemperature.

In the ceramic heaters according to Examples 4, 5 and ComparativeExample 2, the silicon wafer was placed by way of the lifter pins. Thus,free particles were hardly generated. However, in the ceramic heateraccording to Comparative Example 3, the ceramic heater was scrubbed withthe plugs made of AlN at the time of the heating, so that a large amountof free particles were generated in the silicon wafer.

EXAMPLE 6

In the present Example 6, a ceramic heater was produced in the same wayas in Example 4 except that the ratio of the diameter of thediameter-increasing portion in the heating face and the columnar portionwas changed.

A silicon wafer having thermocouples was placed on the produced ceramicheater through the lifter pins, and then the wafer was heated to 300° C.The difference between the highest temperature and the lowesttemperature in the silicon wafer was examined. The result is shown inFIG. 16.

In FIG. 16, the vertical axis ΔT represents the temperature difference(° C.) between the highest temperature and the lowest temperature in thesilicon wafer, and the ratio as the horizontal axis represents the ratioof the diameter of the diameter-increasing portion at the heating faceof the ceramic heater to the diameter of the columnar portion (thediameter of the diameter-increasing portion/the diameter of the columnarportion).

As is clear from FIG. 16, if the ratio of the diameter of thediameter-increasing portion in the heating face to the diameter of thecolumnar portion is less than 1.2 or exceeds 10, the temperaturedifference ΔT in the silicon wafer gets large.

EXAMPLE 7 Production of Electrostatic Chuck (See FIGS. 21 to 22)

(1) The following paste was used to perform formation by a doctor blademethod, so as to form a green sheet having a thickness of 0.47 μm: apaste obtained by mixing 100 parts by weight of aluminum nitride powder(manufactured by Tokuyama Corp., average particle diameter: 1.1 μm), 4parts by weight of yttrium (average particle diameter: 0.4 μm), 12 partsby weight of an acrylic resin binder, 0.5 part by weight of a dispersantand 53 parts by weight of alcohols of 1-butanol and ethanol.

(2) Next, this green sheet 100 was dried at 80° C. for 5 hours, andsubsequently the following were produced: a green sheet to which noprocessing was applied; a green sheet in which through holes for viaholes, for connecting heating elements to conductor circuits, wereformed by punching; a green sheet in which through holes for via holes,for connecting the conductor circuits to external terminals, were formedby punching; and a green sheet in which through holes for conductorfilled through holes, for connecting electrostatic electrodes to theexternal terminals, were formed by punching.

(3) The following were mixed to prepare a conductor containing paste A:100 parts by weight of tungsten carbide particles having an averageparticle diameter of 1 μm, 3.0 parts by weight of an acrylic resinbinder, 3.5 parts by weight of α-terpineol solvent, and 0.3 part byweight of a dispersant.

The following were mixed to prepare a conductor containing paste B: 100parts by weight of tungsten particles having an average particlediameter of 3 μm, 1.9 parts by weight of an acrylic resin binder, 3.7parts by weight of α-terpineol solvent, and 0.2 part by weight of adispersant.

(4) The conductor containing paste A was printed on the surface of thegreen sheets in which the through holes for the via holes were formed byscreen printing, so as to print a conductor containing paste layer whichwould be the heating elements. The conductor containing paste A wasprinted on the surface of the green sheets in which the through holesfor the conductor filled through holes, for connecting the conductorcircuits to the external terminals, were formed by screen printing, soas to print a conductor containing paste layer which would be theconductor circuits. A conductor containing paste layer having anelectrostatic electrode pattern having the shape illustrated in FIG. 23was formed on the green sheets to which no processing was applied.

Moreover, the conductor containing paste B was filled into the throughholes for the via holes, for connecting the heating elements to theconductor circuits, and the through holes for the conductor filledthrough holes, for connecting the external terminals.

Next, the respective green sheets which had been subjected to theabove-mentioned processing were laminated.

First, thirty four green sheets in which only the portions which wouldbe the conductor filled through holes 93 were formed were laminated onthe upper side (heating face side) of the green sheet on which theconductor containing paste layer which would be the heating elements wasprinted, and then the green sheet on which the conductor containingpaste layer which would be the conductor circuits was printed waslaminated on the just lower side thereof (bottom face side).Furthermore, twelve green sheets in which the portions which would bethe conductor filled through holes 93, 930 and 930′ were formed werelaminated on the lower side thereof.

The green sheet on which the conductor containing paste layer having theelectrostatic electrode pattern was printed was laminated on the topmostportion of the thus-laminated green sheets, and further two green sheetsto which no processing was applied were laminated thereon. The resultantwas pressed at 130° C. and a pressure of 8 MPa to form a lamination.

(5) Next, the resultant lamination was degreased at 600° C. in theatmosphere of nitrogen gas for 5 hours and then hot-pressed at 1890° C.and a pressure of 15 MPa for 3 hours to yield a nitride aluminum plate 3mm in thickness.

This was cut off into a disk of 230 mm in diameter to prepare a ceramicsubstrate 91 having therein the heating elements 920 having a thicknessof 5 μm and a width of 2.4 mm, the conductor circuits 980 having athickness of 20 μm and a width of 10 mm, and the chuck positiveelectrostatic layer 92 a and the chuck negative electrostatic layer 92 bhaving a thickness of 6 μm.

(6) Next, the ceramic substrate 91 obtained in the (5) was ground with adiamond grindstone. Subsequently, a mask was put thereon, and blasttreatment with glass beads was conducted to form bottomed holes 900 forthermocouples in the surface. The portions above the formed conductorfilled through holes 93 and 930 were hollowed out in the bottom face 91b of the ceramic substrate 91 so as to form blind holes 990.

(7) A composition obtained by mixing 100 parts by weight of aluminumnitride powder (manufactured by Tokuyama Corp., average particlediameter: 1.1 μm), 4 parts by weight of yttria (average particlediameter: 0.4 μm), 11.5 parts by weight of an acrylic resin binder, 0.5part by weight of a dispersant and 53 parts by weight of alcohols of1-butanol and ethanol was used to produce granules by spray-drying. Thegranules were put into a pipe-form mold and sintered at 1890° C. under anormal pressure to produce a cylindrical ceramic body having a length of200 mm, an outer diameter of 45 mm and an inner diameter of 35 mm.

(8) To bonding faces of the ceramic substrate 91 and the cylindricalceramic body 97 was applied a liquid obtained by mixing 100 parts byweight of aluminum nitride powder (manufactured by Tokuyama Corp.,average particle diameter: 1.1 μm), 4 parts by weight of yttria (averageparticle diameter: 0.4 μm), 11.5 parts by weight of the acrylic resinbinder, 0.5 part by weight of the dispersant and 53 parts by weight ofalcohols of 1-butanol and ethanol. Thereafter, an end face of thecylindrical ceramic body 97 was brought into contact with the bottomface 91 b of the ceramic substrate 91 at a position, in a manner thatthe blind holes 990 would be inside the inner diameter, of the end face.The resultant was heated at 1890° C. to bond the ceramic substrate 91and the cylindrical ceramic body 97.

Specifically, a mask 190 in which an opening 191 as illustrated in FIG.27 was formed was put on the bottom face of the ceramic substrate 91.Thereafter, the cylindrical ceramic body 97 was fitted into the opening191, and the resultant was heated to bond the ceramic substrate 91 andthe cylindrical ceramic body 97.

The distance L between: the center of the circle surrounded by theinterface between the ceramic substrate 91 and the cylindrical ceramicbody 97; and the center of the bottom face of the ceramic substrate 91was set to 5 μm.

(9) Next, brazing silver (Ag: 40% by weight, Cu: 30% by weight, Zn: 28%by weight, Ni: 1.8% by weight, and the balance: other elements, re-flowtemperature: 800° C.) was used to attach external terminals 960 to theblind holes 990 formed in the cylindrical ceramic body 97. Conductivewires 931 were connected to the external terminals 960 through sockets950.

(10) Thermocouples for temperature-control were inserted into thebottomed holes 900, and silica sol was filled into the holes. The silicasol was hardened and gelation occured at 190° C. for 2 hours to bond thecylindrical ceramic body to the bottom face of the ceramic substrateinside which the electrostatic electrodes, the heating elements, theconductor circuits, the via holes and the conductor filled through holeswere formed. In this way, a ceramic bonded body wherein the ceramicsubstrate functioned as an electrostatic chuck was produced.

EXAMPLE 8 Production of Ceramic Heater (See FIGS. 18 to 19, and 26)

(1) The following paste was used to perform formation by a doctor blademethod, so as to form a green sheet having a thickness of 0.47 μm: apaste obtained by mixing 100 parts by weight of aluminum nitride powder(manufactured by Tokuyama Corp., average particle diameter: 1.1 μm), 4parts by weight of yttrium oxide (Y₂O₃: yttria, average particlediameter: 0.4 μm), 11.5 parts by weight of an acrylic resin binder, 0.5part by weight of a dispersant and 53 parts by weight of alcohols of1-butanol and ethanol.

(2) Next, this green sheet was dried at 80° C. for 5 hours, andsubsequently the following were formed by punching: portions which wouldbe through holes 75, for letting lifter pins for carrying a siliconwafer pass through; portions which would be via holes 860; and portions730, 730′ which would be conductor filled through holes, as illustratedin FIG. 18.

(3) The following were mixed to prepare a conductor containing paste A:100 parts by weight of tungsten carbide particles having an averageparticle diameter of 1 μm, 3.0 parts by weight of an acrylic resinbinder, 3.5 parts by weight of α-terpineol solvent, and 0.3 part byweight of a dispersant.

The following were mixed to prepare a conductor containing paste B: 100parts by weight of tungsten particles having an average particlediameter of 3 μm, 1.9 parts by weight of an acrylic resin binder, 3.7parts by weight of α-terpineol solvent, and 0.2 part by weight of adispersant.

This conductor containing paste A was printed on the green sheets inwhich the portions 860, which would be the via holes, were formed byscreen printing, so as to print a conductor containing paste layer 720for heating elements. The printed pattern was formed into aconcentrically circular pattern as illustrated in FIG. 18. The width ofthe conductor containing paste layer 720 was set to 10 mm, and thethickness thereof was set to 12 μm.

Subsequently, the conductor containing paste A was printed on the greensheet in which the portions 730′, which would be the conductor filledthrough holes, were formed by screen printing. In this way, a conductorcontaining paste layer 780 for conductor circuits was formed. Theprinted shape was a band shape.

Moreover, the conductor containing paste B was filled into the portions860, which would be the via holes, and the portions 730 and 730′, whichwould be the conductor filled through holes.

Thirty seven green sheets in which no conductor containing paste wasprinted were laminated on the green sheet which had been subjected tothe above-mentioned processing, the sheet having the printed conductorcontaining paste layer 720. The green sheet on which the conductorcontaining paste layer 780 was printed was then laminated beneath it.Thereafter, twelve green sheets on which no conductor containing pastewas printed were laminated beneath it. The resultant was pressed at 130°C. and 8 MPa, so as to form a lamination.

(4) Next, the resultant lamination was degreased at 600° C. in theatmosphere of nitrogen gas for 5 hours and then hot-pressed at 1890° C.and a pressure of 15 MPa for 10 hours to yield a nitride aluminum plate3 mm in thickness.

This was cut off into a disk of 230 mm in diameter to prepare a ceramicsubstrate 71 having therein the heating elements 72 having a thicknessof 6 μm and a width of 10 mm, the conductor circuits 78 having athickness of 20 μm and a width of 10 mm, the via holes 860 and theconductor filled through holes 73, 73′.

(5) Next, the ceramic substrate 71 obtained in the (4) was ground with adiamond grindstone. Subsequently, a mask was put thereon, and blasttreatment with glass beads was conducted to form bottomed holes 74 forthermocouples in the surface. The portions above the formed conductorfilled through holes 73, 73′ were hollowed out in the bottom face 71 bof the ceramic substrate 71, so as to form blind holes 79.

(6) A composition obtained by mixing 100 parts by weight of aluminumnitride powder (manufactured by Tokuyama Corp., average particlediameter: 1.1 μm), 4 parts by weight of Y₂O₃ (average particle diameter:0.4 μm), 11.5 parts by weight of an acrylic resin binder, 0.5 part byweight of a dispersant and 53 parts by weight of alcohols of 1-butanoland ethanol was used to produce granules by spray-drying. The granuleswere put into a cylindrical mold and sintered at 1890° C. under a normalpressure to produce a cylindrical ceramic body 77.

(7) To bonding faces of the ceramic substrate 71 and the cylindricalceramic body 77 was applied an aqueous yttrium nitrate (2.61×10⁻¹ mol/L)solution. Thereafter, an end face of the cylindrical ceramic body 77 wasbrought into contact with the bottom face 71 b of the ceramic substrate71 at a position, in a manner that the blind holes 79 would be insidethe inner diameter, of the end face. The resultant was heated at 1890°C. to bond the ceramic substrate 71 and the cylindrical ceramic body 77.

Specifically, a mask 190 in which an opening 191 as illustrated in FIG.27 was formed was put on the bottom face of the ceramic substrate 71.Thereafter, the cylindrical ceramic body 77 was fitted into the opening191, and the resultant was heated to bond the ceramic substrate 71 andthe cylindrical ceramic body 77.

The distance L: between the center of the circle surrounded by theinterface between the ceramic substrate 71 and the cylindrical ceramicbody 77; and the center of the bottom face of the ceramic substrate 71was set to 190 μm.

(8) Next, brazing silver (Ag: 40% by weight, Cu: 30% by weight, Zn: 28%by weight, Ni: 1.8% by weight, and the balance: other elements, re-flowtemperature: 800° C.) was used to attach external terminals 83 to theblind holes 79 formed in the cylindrical ceramic body 77. Conductivewires 830 were connected to the external terminals 83 through sockets85.

(9) Thermocouples for temperature-control were inserted into thebottomed holes 74, and silica sol was filled into the holes. The silicasol was hardened and gelation was occurred at 190° C. for 2 hours tobond the cylindrical ceramic body to the bottom face of the ceramicsubstrate inside which the heating elements, the conductor circuits, thevia holes and the conductor filled through holes were formed. In thisway, a ceramic bonded body wherein the ceramic substrate functioned as aceramic heater was produced.

EXAMPLE 9

A ceramic bonded body was produced in the same way as in Example 7except that the following steps were carried out.

First, the diameter of the ceramic substrate was set to 300 mm, and inthe step (7) 100 parts by weight of aluminum nitride powder, 4 parts byweight of yttria, 11.5 parts by weight of an acrylic resin binder, 0.5part by weight of a dispersant and 53 parts by weight of alcohols weremixed to produce granules by spray-drying. Moreover, conductive wireswere bonded to external terminals through sockets to form power sourcesupplying lines. The power source supplying lines were put into a mold,and the granules were filled into the mold, and then pressed.Furthermore, the granules were subjected to cold isostatic press at apressure of 1000 kg/cm², and then sintered at 1890° C. under a normalpressure. The resultant was then shaped into a ceramic body formed of acolumnar sold body having a length of 200 mm and an outer diameter of 45mm.

The distance L between: the center of the bottom face of the ceramicsubstrate; and the center of the interface between the ceramic body andthe ceramic substrate was set to 3 μm.

EXAMPLE 10

A ceramic bonded body was produced in the same way as in Example 8except that the following steps were carried out.

The diameter of the ceramic substrate was set to 320 mm, and in the (6)100 parts by weight of aluminum nitride powder, 4 parts by weight ofyttria, 11.5 parts by weight of an acrylic resin binder, 0.5 part byweight of a dispersant and 53 parts by weight of alcohols were mixed toproduce granules by spray-drying. Moreover, conductive wires were bondedto external terminals through sockets to form power source supplyinglines. The power source supplying lines were put into a mold, and thegranules were filled into the mold, and then pressed. Furthermore, thegranules were subjected to cold isostatic press at a pressure of 1000kg/cm², and then sintered at 1890° C. under a normal pressure. Theresultant was then shaped into a ceramic body formed of a columnar soldbody having a length of 200 mm and an outer diameter of 45 mm.

The distance L between: the center of the bottom face of the ceramicsubstrate; and the center of the interface (circle) between the ceramicbody and the ceramic substrate was set to 200 μm.

EXAMPLE 11

A ceramic bonded body was produced in the same way as in Example 7except that L was set to 10 μm.

EXAMPLE 12

A ceramic bonded body was produced in the same way as in Example 8except that L was set to 50 μm.

EXAMPLE 13

A ceramic bonded body was produced in the same way as in Example 9except that L was set to 100 μm.

EXAMPLE 14

A ceramic bonded body was produced in the same way as in Example 10except that L was set to 150 μm.

TEST EXAMPLE 2

Ceramic bonded bodies wherein L was changed from 0 to 240 μm wereproduced. The temperatures of the ceramic bonded bodies were risen to450° C. At this time, the temperature difference ΔT between the highesttemperature and the lowest temperature in the heating face was measured.The results are shown in FIG. 31. It is understood that when L was morethan 200 μm, ΔT got large. The ceramic bonded bodies had the sameconstitution as illustrated in FIGS. 18 to 19.

COMPARATIVE EXAMPLE 4

A ceramic bonded body was produced in the same way as in Example 7except that the ceramic substrate 91 was bonded to the cylindricalceramic body 97 in such a manner that the center of the circlesurrounded by the interface between the ceramic substrate 91 and thecylindrical ceramic body 97 and the center of the bottom face of theceramic substrate 91 would be at the same position.

COMPARATIVE EXAMPLE 5

A ceramic bonded body was produced in the same way as in Example 7except that the distance L between: the center of the circle surroundedby the interface between the ceramic substrate 91 and the cylindricalceramic body 97; and the center of the bottom face of the ceramicsubstrate 91 was set to 2 μm.

COMPARATIVE EXAMPLE 6

A ceramic bonded body was produced in the same way as in Example 8except that the distance L between: the center of the circle surroundedby the interface between the ceramic substrate 71 and the cylindricalceramic body 77; and the center of the bottom face of the ceramicsubstrate 71 was set to 2 μm.

COMPARATIVE EXAMPLE 7

A ceramic bonded body was produced in the same way as in Example 7except that the distance L between: the center of the circle surroundedby the interface between the ceramic substrate 91 and the cylindricalceramic body 97; and the center of the bottom face of the ceramicsubstrate 91 was set to 205 μm.

COMPARATIVE EXAMPLE 8

A ceramic bonded body was produced in the same way as in Example 8except that the distance L between: the center of the circle surroundedby the interface between the ceramic substrate 71 and the cylindricalceramic body 77; and the center of the bottom face of the ceramicsubstrate 91 was set to 205 μm.

The ceramic bonded bodies according to Examples 7 to 14 and ComparativeExamples 4 to 8 were subjected to the following evaluation tests. Theresults are shown in Table 3 described below.

(1) Measurement of the Breaking Strength

A bending strength test was performed to measure the breaking strengthof the bonding face.

(2) Heat Cycle Test

A heat cycle test wherein the step of keeping each of the ceramic bondedbodies at 25° C. and then heating it to 450° C. was repeated was made500 times. It was checked whether or not a crack was generated in thebonding portion between the cylindrical ceramic body and the ceramicsubstrate. A case in which the generation rate was less than 50% wasjudged as no generation of any crack, and a case in which the generationrate was 50% or more was judged as crack generation.

(3) Existence of Corrosion in the Wires and so on

Each of the ceramic bonded bodies according to the Examples and theComparative Examples was fitted to a supporting case, and thetemperature thereof was risen to 200° C. in the atmosphere of CF₄.Thereafter, the state of corrosion in the wires and so on of the ceramicbonded body was observed with the naked eye.

Nitrogen gas was introduced, as an inert gas, into the cylindricalceramic body. TABLE 3 Breaking strength (MPa) Heat cycle test CorrosionExample 7 400 No generation of Not generated crack Example 8 410 Nogeneration of Not generated crack Example 9 440 No generation of Notgenerated crack Example 10 435 No generation of Not generated crackExample 11 411 No generation of Not generated crack Example 12 405 Nogeneration of Not generated crack Example 13 438 No generation of Notgenerated crack Example 14 430 No generation of Not generated crackComparative 320 Crack generation Generated Example 4 Comparative 300Crack generation Generated Example 5 Comparative 285 Crack generationGenerated Example 6 Comparative 320 Crack generation Generated Example 7Comparative 300 Crack generation Generated Example 8

As is evident from the results shown in Table 3, the ceramic bondedbodies according to Examples 7 to 14 had sufficiently large bondingstrength in both of the breaking strength test and the heat cycle test,and the wires and so on arranged inside the cylindrical ceramic bodiesof these ceramic bonded body were not corroded by CF₄ gas.

On the other hand, in the ceramic bonded bodies according to ComparativeExamples 4 to 8, the bonding strength between the cylindrical ceramicbody and the ceramic substrate was low, and further the wires and so onarranged inside the cylindrical ceramic body were corroded by CF₄ gas.

It appears that this is because thermal stress concentrated locally inthe bonding interface between the cylindrical ceramic and the disk-likeceramic, whereby thermal fatigue was generated so that cracks and thelike were generated.

EXAMPLES 15 AND 16, AND COMPARATIVE EXAMPLES 9 AND 10

L was set to 3 (Example 15), 200μm (Example 16), 0 μm (ComparativeExample 9) and 205 μm (Comparative Example 10), respectively, and thediameter of a ceramic substrate was changed from 150 mm to 350 mm. Thecrack generation rates of the thus-produced ceramic bonded bodies wereexamined. The results are shown in FIG. 32.

As is evident from Comparative Examples 9 and 10, the crack generationrate was close to 80% when the diameter was more than 250 mm andpractical endurance was not obtained. On the other hand, in Examples 15and 16, the value of the crack generation rate was kept low even if thediameter was more than 250 mm. As described above, the present inventioncan overcome endurance drop generated in ceramic heaters having adiameter of 250 mm or more.

Industrial Applicability

According to the ceramic heater of the first aspect of the presentinvention, three or more through holes are formed in a ceramic substrateand formed in an area whose distance from the center of the ceramicsubstrate is ½ or more of the distance from the center to the outer edgethereof; therefore, lifter pins passed through the through holes arealso present in the peripheral portion of the ceramic substrate and donot concentrate in the central portion. Thus, a semiconductor wafersupported by the lifter pins and the like does not become unstable.

A difference in the heat capacity in the ceramic substrate is small sothat a dispersion in the temperature thereof is small when thetemperature is risen. Thus, a semiconductor wafer or the like can beevenly heated.

According to the ceramic heater of the second aspect of the presentinvention, in through holes formed in a ceramic substrate, the diameterthereof on the side of its heating face for heating an object to beheated is larger than that on the side opposite to the heating face;therefore, the occupation rate of gas in portions where cooling spotsare generated gets large so that the heat capacity thereof gets small.Accordingly, the temperature of a semiconductor wafer, a liquid crystalsubstrate and the like of the portion in the vicinity of the formedthrough holes hardly drops so that the object to be heated, such as thesemiconductor wafer or the liquid crystal substrate, can be more evenlyheated.

Furthermore, according to the ceramic bonded body of the third aspect ofthe present invention, thermal stress does not concentrate locally inthe bonding interface between a ceramic body having a given shape suchas a cylindrical or columnar shape and a disk-like ceramic so that nocrack and the like are generated in this portion; therefore, sufficientair-tightness can be kept. Thus, the reliability of the ceramic bondedbody can be largely improved.

1. A ceramic heater comprising: a disk-like ceramic substrate; a heatingelement formed on a surface of or inside said ceramic substrate; andthrough holes for letting lifter pins pass through at said ceramicsubstrate, wherein three or more of said through holes are formed, andsaid through holes are formed in an area whose distance from the centerof said ceramic substrate is ½ of more of the distance from the centerof said ceramic substrate to the outer edge of said ceramic substrate.2. The ceramic heater according to claim 1, wherein said through holesare formed at substantially regular intervals on a single circle whichhas a concentric circle relationship with said ceramic substrate.
 3. Aceramic heater comprising: a disk-like ceramic substrate; a heatingelement formed on a surface of or inside said ceramic substrate; andthrough holes for letting lifter pins pass through at said ceramicsubstrate, wherein the diameter of each of said through holes on aheating face side for heating an object to be heated is larger than thediameter of said through hole on the side opposite to said heating face.4. The ceramic heater according to claim 3, wherein each of said throughholes comprises a columnar portion and a diameter-increasing portion,the diameter of said diameter-increasing portion becomes larger as theportion is closer to the heating face.
 5. The ceramic heater accordingto claim 3, wherein the diameter on the heating face side of each ofsaid through holes is from 1.2 to 10 times as large as the diameter onthe side opposite to said heating face of said through holes.
 6. Aceramic bonded body comprising: a disk-like ceramic substrate insidewhich a conductor is provided; and a ceramic body bonded to the bottomface of said ceramic substrate, wherein the center of an area surroundedby the interface between said ceramic body and said ceramic substrate,or the center of an area constituted by the interface between saidceramic body and said ceramic substrate is 3 to 200 μm apart from thecenter of the bottom face of said ceramic substrate.
 7. A ceramic bondedbody comprising: a disk-like ceramic substrate inside which a conductoris provided; and a cylindrical ceramic body having a cylindrical shapebonded to the bottom face of said ceramic substance, wherein the centerof the circle surrounded by the interface between said cylindricalceramic body and said ceramic substrate is 3 to 200 μm apart from thecenter of the bottom face of said ceramic substrate.
 8. The ceramicbonded body according to claim 6, wherein said conductor is a heatingelement, and functions as a hot plate.
 9. The ceramic bonded bodyaccording to claim 6, wherein said conductor is an electrostaticelectrode, and functions as an electrostatic chuck.
 10. The ceramicbonded body according to claim 6, wherein said ceramic substrate has adiameter of 250 mm or more.
 11. The ceramic heater according to claim 4,wherein the diameter on the heating face side of each of said throughholes is from 1.2 to 10 times as large as the diameter on the sideopposite to said heating face of said through holes.
 12. The ceramicbonded body according to claim 7, wherein said conductor is a heatingelement, and functions as a hot plate.
 13. The ceramic bonded bodyaccording to claim 7, wherein said conductor is an electrostaticelectrode, and functions as an electrostatic chuck.
 14. The ceramicbonded body according to claim 7, wherein said ceramic substrate has adiameter of 250 mm or more.